Snakes.... I have had all kinds of triggers chew on my live rock. But, the undulated I have seen do some plain crazy things. As far as the powerhead.... there were a couple of incidents. The first undulated chewed all the power cords on the power heads, heaters, and everything else. He also would pull on the tank's seals. So he left.
The second one used to take the strainer off my powerhead and swim around the tank with it. Then he chewed it up so I took it out. After that, he chewed up the fan to aim the water flow. Then he started working on the acutal powerhead. There were big gashes in it, and cuts, and it was just bad. Still worked, but would shake and make noise. So I got rid of it, and the undulated.
These were large undulateds though, about 6-7 inches. I kept my aggressives in a 200 gallon tank. I almost got an undulated that was about 16 inches. He was amazing. But, I decided against it. I was going to have him, my extra large clown trigger, and another large trigger. BUt, instead, went to smaller ones. Craziness.