I would leave the collar on at this age, but I would only be practicing with the leash at this point. I would at this age allow the puppy to play with the leash and even teeth on it so that the leash is positive, I would wait until around 4 or 5-months-old to correct that. Carrots are great for teething puppies. I don't actually clip a leash on a collar until 3-months-old. You can try the command "shame" but I think you might just try giving it some time. Remember it is only 5 minutes for each month of age with the walk with puppies, so an 8-week-old puppy only gets a 10 minute walk. Too much walking is bad for legs and joints. When my puppies are first little, I practice with the leash. In the house, I drape the leash on them and try to call them to me. Outside, I practice in my fenced back yard for about a month before the puppy graduates to the street. I might drape the leash on the puppy and get him to follow me, or drag the leash on the ground and see if he will follow me and try to catch the leash. There are many things in my back yard that scare a puppy, so it is so much easier to address, or correct issues when I am in my back yard and not in the street. We just walk laps in the yard and deal with drama as it comes up. Maybe around 3-months-old I might try to clip the leash to the collar, but if there is too much protesting, I drop the leash. They just get better with the leash around 4 to 5-months-old. So anyway, I use the commands "go" when I want to "go" and if the puppy tugs on the leash, I stop and say "wait". It is my walk and we go as fast as I can walk and no faster. If I want to "wait" and look at a flower, change the batteries in my walkman, count to ten, then I do it, it is my walk. When I am ready I say "go" and we "go" again. When the puppy pulls on the leash, I stop and say "wait" and we stop again, even if we just went two steps. I praise the puppy when he is doing good and talk soothing to him and encourage him when he is doing good, so he keeps doing it. It takes several laps of "go" and "wait" until he settles down, and when the walk is over, I make a big fuss and clap and then they get some play time. They don't like the walk at first, but they like the fuss at the end. I have to address "go" and "wait" again the next day, but it won't take me as long to get him to understand what I want from him. I also house sat a dog, and the owner thought he had leash issues, and that dog just didn't like being in front. He walked just fine with my dogs as long as he could be part of the group, but he didn't want to be in the front. If you have a family member, or a neighbor that has a dog that walks well, see if you can practice with them. I also had one dog that didn't like the maroon leash, or the pink one, but did just fine with the blue leash. Sometimes puppies are just puppies.