wallhack is something you can't get around, a user can always control how their graphics are displayed, hence you can't trust them. You either accept this or change the game.

You can make it harder to do (Blizzard's Warden, Valve's VAC) but people will get around any technical barrier you put up.

Fog of War (maphack) would be a more apt example, you only send the client what it is possible for them to see. Speed hacks are another that can be stopped, the client asks the server if it can move X units, the server responds with how many units the client moved.