Perk should never have been put on Z-Bo in the first place. He simply doesn't have the quickness or agility to cover an offensive threat like Z-Bo.
Randolph's jump shooting, pick and roll/pop game, ability to put the ball on the floor and drive + Randolph's superior quickness/agility make Perk an ineffective defensive matchup.
Leave Perk on Marc Gasol. A player who he can actually defend.