I have a customer who has a very nice water feature that was obviously installed some years ago. It works fairly well. But we've figured out that the second tier of the pond has a big leak. Not quite sure where the leak is. But we know it's in that second tier because when you turn the water feature off, water stays full in the upper tier and lower tier but the middle pond empties out about half-way. No obvious holes. There are several minor cracks going up the walls of the pond on this second tier. But none of them go only half way down and none of them appear to be the smoking gun that is causing the leak. To make matters more difficult, when it is turned on and starts leaking, it's not clear where the water is going. There is never any pooling of water underground or above ground anywhere. It's as if the water is just disappearing under ground. The customer wants to repair it himself. Which is fine by me. We're doing tens thousands of dollars of work for him in other parts of his landscape. But I'd like to direct him toward a product that he could use. I am looking for something that he could apply to the walls of that second tier that would just re-seal everything. Pond liner isn't an option. It wouldn't work with this water feature. We need something that can be applied right to the walls. The walls on the entire water feature are concrete or gunite or something like that. So it would be nice if we could use a product that would match that gray color. But I think he's open to any product. I am thinking something that could be sprayed or applied with a brush, roller, or trowel. Any ideas guys? And if you could also tell me where, ONLINE, I could buy it that would be bonus! Thanks!