Once a boat is built, the best you can do as an owner is to make sure the bilge is staying dry, ie your pumps are working right and you stop/prevent any leaks from anywhere coming into your boat. All your thru-holes, engine bolts, self tapping screws etc need to be properly bedded/sealed with marine caulk made for below the waterline like a 5200 and/or epoxy. Best of all, if you can avoid drilling into the transom, don't. I made a fairing block large enough and contoured like the hull bottom and epoxied it to the transom and then screwed my transducer into it. The mounting screws will never see the wood in the transom and if the block ever gets punky, I'll grind it off and make a new one. Drain your fuel tank area regularly as well. And cover your boat in the winter.....if not, little by little water weeps in somewhere, and as Bob mentioned above, once the freeze thaw theory takes place, it pretty much becomes unstoppable.