Many times I'll find myself in a situation that while doing retopology, some vertices will snap on the back of the model instead of the side I'm editing. First of all I wanted to ask if there is a way to avoid this misshap, and second I was wondering if there is a way to move those vertices back where I want (move tool most of the times won't work in this situation), or do I have to delete the polygon they belong to, and rebuild it?