You are going to want two separate “walls” and “sweepers”. A wall can take hits, where as a sweeper can potentially take out your opponents entire team, or “sweeping” them away. You want two for the sake of hitting your opponent in both physical and special attacks, and being able to take the hits your opponent dishes out. This article will focus on your wall. A good Pokémon that can double as a physical and special wall is Pokémon #042 Golbat. The EV (effort value) spread should look like this:
Held Item: Eviolite
Special Attack: 0
Special Defense: 252
This is a wall I use in competitive play, and it works great if used properly.