Have a leaky canister filter or media reactor that doesn’t leak enough to replace but leaks just enough to be annoying? If the equipment can’t be fixed by replacing consumable parts like O-rings or other inexpensive pieces, try placing a small plastic container under it. This will allow you to keep the equipment in operation, while at the same time containing any water and preventing it from getting on any of the other equipment powering your aquarium. The container will have to be cleaned and drained from time to time, but it beats having to buy a replacement for the leaky equipment. Obviously anything leaking with significant water at a quick pace should be torn down and replaced immediately.