First, let me say that doing anything to puppies ears before 4 months of age is a waste of time and money. The cartilage doesn't start growing up the ears until the pups are about 5 months old and keeps growing until they're nearly a year old. So, the ears should be stuck down from 4 months until 12 months. That way, as the cartilage grows, it will form to the curve of the taped ear. So, no matter whether your pup's ears are prick or not, wait until 4 months old to start taping.
Over the years, I've tried several different methods of sticking ears down to get that proper tip of the upper ear. The method I'm using now gives me the best results for the least amount of money. Even if money isn't an issue, this method gives the best results I've seen. There's two tapes that I like. Duct tape is the cheaper of the two by far and I find a couple of the cheaper brands work best, rather than the major brands. The reason is, the really good stuff is too thick and won't mold around the ribs in the ears well enough. I use a brand called Fred's. I get it at Fred's department store. However, there aren't very many Fred's stores. This duct tape is thin, cheap, and very sticky. Some cheap brands aren't sticky enough, so when you find a good one, stay with it. Another type of tape which works better is Elasticon surgical tape which is made in South Africa by Johnson & Johnson. However, the cost is much higher, if you can find it at all, but it does stay in a lot longer. The reason is, it's elasticized, so it can move with the ear. I get mine online from the cheapest source. Whichever you use, buy the two inch wide roll. Here's how to use these tapes. The first thing you should do is clean the ears with engine starting fluid, preferably the Prestone brand sold at WalMart. Prestone seems to have the least amount of oily lubricants which will prevent stuff from sticking to the ears. Spray some on a paper towel and clean the ears out, especially if the ears have never been, or haven't been for awhile, stuck down. Don't use alcohol, the tape won't stick well if you do. Cut off a piece of tape nearly 1/2" wide. If using Elasticon, lightly spray just the bottom 1/4" of the piece of tape with starting fluid. If using duct tape, spaying is optional. Stick the unsprayed part of the tape on the upper ear, back side (with hair), with just under 1/2" (the sprayed part) sticking out beyond the tip of the ear. Tip the ear over and stick the sprayed part of the tape to the skin on the inside of the ear just about touching the large cartiledge bump near the base of the ear. Hold for about 10 seconds or so. Cut another piece of tape nearly 1/2" wide and, if using Elasticon, lightly spray the entire length with starting fluid. If using duct tape, spraying if optional. If using Elasticon tape, wait about 30 seconds before using it. Stick that on the inside of the ear across the other piece of tape to anchor it. It should be stuck just down to that cartiledge bump on the inside of the ear. Be sure to mold the cross piece around the ribs in the ear so the entire tape is in contact with skin. Keep pressing the tape for about 30 seconds to insure it's dry and well stuck. The reason spraying duct tape is optional is because duct tape tends to ride up when sprayed. It may stay a little longer if sprayed, but be sure it doesn't ride up before completely dry.
If you have just one pup, this should stay in for several days. If you have more than one pup, it's hard to say how long this will last. With smooth pups, a couple of days or so is it because they grab each others ears all the time playing. It usually stays in longer with rough pups. When the tape unsticks from the inside of the ear, gently remove the part on the hairy backside by peeling it off in the direction that the hair lays, which is toward the tip. If you encounter too much resistance removing Elasticon tape on rough pups, spray a little starter fluid on a paper towel and use it to help separate the tape from the hair. There may be a small amount of residue left in the ears. Just spray some starting fluid on a paper towel and clean it out. It takes just seconds. Then retape the ears. This method gives me the desired natural curl to the ears, rather than a sharp crease that looks like you've fixed the ears. I've also found that it helps the ears stay tipped much longer than sticking them down from the inside with glue or other tapes. The chances of getting ears to permanently tip are higher with this method as well. Of course, on many collies, getting them to be permanently tipped without help is nearly impossible, but the odds are best with this method.
What I described above is my preferred way of tipping the ears. There are many other ways. Most breeders not only stick them down, but also tie them together in hopes of improving the ear set. In other words, they want the ears to be relatively close together. The correct ear set is when the inside edge of the ear lines up with the center of the eye. It's actually impossible to really change the ear set. What's really happening is, the skull side of the ear buckles somewhat when the ears are pulled together. After being tied together for months, that buckle gets to be permanent which "gives the impression" of a closer ear set. The actual ear set hasn't changed a bit. I don't bother to tie my pups ears together. The ear sets on my dogs are within what I believe to be correct. And besides, when there's a string or other object between the ears, the other pups will pull the whole setup out before the day is done.
There are also various types of glues and adhesives people use to stick ears down. I've tried Skin Bond Adhesive. It does stay in longer than taping, but it sure is difficult to get that glue out when it comes undone. On tough to tip ears, I've seen them go almost prick again by the time I got all the glue out. You will loose hair also. No Sew is another glue commonly used, but most folks that use it glue the hair from the tip of the ear to some long hair from the base of the ear. Can't do that with smooths. I have a friend that uses Val-A Chicago Tear Mender Fabric-Leather Cement on his smooths. He says it works great, but spends a lot of time getting it all out. He uses Surgical & Sports Tape Remover or engine starting fluid to clean it out of the ears. Again though, it's a long and tedious job to get that glue out. Another product commonly used over the years is mole skin. That's what we were taught to use years ago. It's used on the inside of the ear which causes a sharper crease in the ear. It really doesn't work any better than tape, it just costs a whole lot more. In the case of weak ears that won't come up enough, mole skin can be used to help hold them up. Cut an egg shaped piece of mole skin, spray the entire glue side of the skin with starting fluid, and stick that in the ear, narrower side down, just to that big cartiledge bump. The larger top end of the skin should be cut so it ends just below where the natural tip should be. You can then tape the tip down with duct tape, as in the first paragrapgh, but don't spray the tape and don't use a cross anchor. When the mole skin comes loose, you want it to break away from the duct tape or all the weight will pull the ear way down again.
So you see, there's many different substances used to stick ears down. I've tried most of them. The duct tape is the most economical to use and the residual sticky stuff left in the ear when it comes undone is very quickly and easily removed with starting fluid sprayed on a paper towel. But, it doesn't stay in as long as glue. I prefer the easy cleanup and economy, plus the more natural look I get using tape. At dog shows, we do the same thing to hold the ears over overnight, but we don't use the starting fluid. Without the starting fluid, the tape peels off clean, no residue to clean out. But it doesn't stick very well. It will probably come out if the dogs play.