Well I don't know if you mean defog through level up or through the hm but these two make real good use of defog:
Mandibuzz
Overcoat
Rocky Helmet
Foul play
Defog
Roost
Taunt
Latias
Levitate
Leftovers
Roost
Dragon pulse
Psyshock
Defog
These two both can take really good hits but one is for special walling and the other physical so depending on your team should you put one on your team.(just so you know latias is the special wall and mandibuzz is (usually) a physical wall)
