My parents have a really small old concrete koi pond in there back patio. they never did anything fancy with it just koi and goldfish. this years drought and water restrictions and lack of maintenance caused it to dry up. sometime during the summer it developed a few cracks and now it wont hold water. its empty and cleaned out now. what is a easy and cost effective product i can use to seal all the cracks and maybe re coat the whole pond? it looks like at sometime someone re coated it with some kind of concrete/plaster? I just want to get it to hold water again.