We All Want That Magic Bullet To Keep Mice Away!

But What Actually Works And What Are We Wasting Our Time With?
Foam & Caulk
Foam and Caulk may not taste all that appealing but if a mouse wants to see the other side of it it won't take much for them to motor through it.
Copper Mesh
Famed for being plentiful, cheap and easy to shove in holes this combined with foam and caulk can be a decent solution for some types of holes. On its own there are issues.