I had problems with a few fish jumping into the overflows. I got some plastic gutter guard from Home Depot and cut it to make a "fence" around the overflow boxes and it seems to have corrected the problem.
On a side note, we have three tanks in a horseshoe arrangement with a common sump. One morning (before the gutter guard) we noticed a small chromis in the wrong tank. He looked like he's been run over by a weed-eater. We realized the only way he could have gotten there is to have gone down the overflow, through the sump, got sucked up by the return, gone through the pump, and got diverted to that tank by the chance of negotiating the forks in the manifold on the return pump. He was swimming fine and has healed from all his "bruises" and doing fine to this day. Since then two other fish have shown up in the "wrong" tank. I never would have believed they could have lived through the ordeal of being slapped through a Sequence pump. Actually, it may have happened more times than I know as they would have a 33% chance of being spit out in the same tank they came from.
