Allied takeovers

[Thulsa Fucking Doom]

Sometimes I like to play 2v2v2 with an AI on my team, but it is frustrating that you can take your ally's square by walking over them.
I do garrison things like mines with a unit or two to prevent this, but what about when you play a faction that takes advantage of common squares like forests and swamps?
I'm sure there is a mod to fix this, but it is an annoying feature in the vanilla game.

[Farsight]

Have you tried playing both Classes yourself?