I use Toxapex as a wall, it's fairly good, because it has high defense and special defense stats. And it's signature move is some protect with a poisoning effect. It's also handy that it learns recover. However Toxapex has some disadvantages, it has problems against steel and poison types. Electric, ground and psychic Sweepers are troublesome.
Other good tanks are Shuckle (in previous generations), Bastiodon, Metagross, Carbink, Probopass, Dusknoir (in previous generations), Aegislash (can be used as a tank),