You should be able to buy a resonable fiberglass repair kit in your hardware store or ir not try a RV dealer ( They sell a repair kit for fiberglass water tanks that should do the trick.) Failing that since you are only going to use it for a water garden. You should be able to repair any cracks in the fiberglass with plain old epoxy. This may not be as pretty but it will definitely serve the purpose and should look OK with a coat or two of paint. Good luck....