As any trainer can attest, this is usually a fairly straightforward exercise…most of the time. I had taught dozens of pups the basics of how to sit and stay without any difficulty.
My typical “go-to” plan for teaching this skill is as follows: Ask the dog to sit. Give a hand signal and verbal cue to stay, and immediately reward before he has a chance to move. Praise and release.
Once this is going well, I can begin to pause briefly after giving the cue – then reward. First one second, then two, then three. Etc. I add distance very gradually once the dog is solid for several seconds with me standing in front.
For most dogs, this is a fun and effective way to build the beginnings of a good stay behavior. Done correctly, in the early stages, there’s almost no opportunity for the dog to make a mistake – he’s too busy being rewarded for being right. If he does happen to get distracted and pop up too early, I simply reset and try again. Most of the pups in my classes catch on very quickly, and have a good start on this skill by the end of the first session.