Stand has always been one of those things that's given him trouble to get exact. He'll stand up, but then he'll continue to come towards me, or proceed to sit back down once I mark and reward him. Standing from a sit also gives him problems for some reason and sometimes when I want him to stand or when I ask him to stand after sitting down on his own (i.e. I want him to stand back up), he'll act as though he doesn't know how to do it.
As such, I've tried to think of ways to "explain" this to him again.
From A Sit:
One thing that's helped was teaching him walk backwards, especially doing so from a sit. This required him to "pop up" his rear in order to move backwards. Repeating this got him in the habit of "popping up" when asked to stand from the sit position. Doing this also prevented him from moving forward as his front paws don't need to move at all, except maybe to slightly re-balance his weight a bit. This is much better than the old way where he would take a step forward in order to stand from a sit.
Sometimes, throwing a "stay" right after would help. The idea would be to get him to anticipate the stay right after standing, causing him to freeze. However, this gave mixed results because sometimes, he'd be going into a walk right as he stands. This might do nothing be stop him after taking a step, when I want no steps at all.
From A Down:
Standing from a down is much easier for him, especially once he learned the fold-back method of going down. The stand is just the reverse of this, making it easy for him to get some muscle memory for getting into position.
The big problem here is again the moving forward, and it's even worse here because the reverse of the fold-back has his body's weight moving forward, making it natural for him to start walking forward. To help counter this, I asked for the stand while being very close to him, giving him no room to move forward. Hopefully, this starts to teach his body how to control the weight shift and "unfold" while staying put, except again to shift his paws to maintain more comfortable balance.
For now, I still have to work close to him doing this, but I have begun moving back from him to start generalizing the distance so that he doesn't think he stays put only when I'm right up on him. The last time we did this, I was maybe three or four feet away from him and he didn't move forward when he stood up. Looks like we're making some early progress in this regard, but there's more work to do.
Also, for now, there's no Spanish cue for this. Sit, Stand, Speak, and Drop (lie down) don't have a Spanish cue connected to them yet. For stand, I want to work on the behavior more, for the others...well...I don't know why not!