I have a faux rock grotto feature that reaches below the water level 24x7. Last summer while swimming I noticed a couple dime sized rust spots underwater and on the faux rock area. I drained about 1/4 of the pool to gain access to the spots. I used a cement drill bit, drilled the rust off, and patched it with rapid setting waterproof cement - this stuff would begin to set if I left it mixed for more than 2 minutes. Of the 4 spots I repaired, one didn't seem to work and I'm wondering if I didn't patch thoroughly enough and water continues to get through. And I recently just found a few more pencil eraser-sized spots on another area that also sits below the water line 24x7. I'm draining my pool tonight due to high CYA and am going to tackle these rust spots again. Just looking for some anecdotal advice on what I should and shouldn't do during this next round.