I had an epic tactic for monkey rounds on my round 28 solo play through.
I basically had Juggernaut, PhD flopper, Stamin-up and Quick revive and was able to protect them all at once.
What I did was: luckily, I managed to buy quick revive for the last time before a monkey round, so the machine dissappeared, leaving me with the perk and the monkeys with no way of attacking it. So that was 1 perk automatically covered.
With stamin-up, I would save a zombie 1 round before I was ABSOLUTELY sure it was Monkeys next. I then went and lead the zombie as close to the stamin up as possible and proceeded to kill him. When the monkey round started, I planted 2 claymores by stamin-up and on the way back to juggernaut/PhD flopper, I activated the fire trap. So that was 2 perks covered.
Then, with Juggernaut and PhD flopper, I stood in the doorway connecting the 2. (The door next to the MP5K) I killed as many as I could there and then went and double checked Juggernaut and then PhD flopper.
That's how I got to round 28 solo and still kept all 4 of my perks.