Stopping character from walking on grass

Hey This is a strange question, but I have a lowpoly map terrain that is essentially just grass with paths on them. The whole terrain is a model by the way. The paths and grass are obviously separate models. However I wanted the player to stay on the paths--so if they tried to move onto the grass it blocks them. Is there a way to block movement like this? Like if the character walks on a certain material it blocks them off like a collider? I mean I could put a hundred different colliders in the map but that would take weeks and possibly cause problems walking on the paths considering it's so complicated...it feels like I could do something easier. I removed the mesh collider on the grass but obviously the player will just fall through. Any ideas? Thanks!