Players keep falling through terrain?

Okay so here's my problem. I'm making a game that involves players using build tools to mess with terrain. My problem though is that people will troll other players by placing terrain on top of the player causing the game to think that the player isn't on solid ground and makes them fall. I know I could probably fix this by adding a piece to the tool that tells it to not place terrain if a player is present in that area. But I want to go with the more difficult route and see if I can make it so either the player is pushed away from the terrain block that is made or is teleported to the surface if surrounded by terrain. If anyone has experience with working with terrain physics please help