I am not sure about the best way of finding the leak, but I know of one way, I haven't done it myself. You can use some phenol red for testing pH, swim very carefully to where you think the leak is trying not to stir the water, and squeeze a little red out near the leak and see if it gets drawn out of the pool. You can't have your pump going, you want as little water disturbance as possible. Being as its 10 feet down, that brings me back to lifeguard training.

As far as getting the patch down to the leak, you can apply the adhesive to the patch and the fold it in half, swim down and unfold the patch and apply. That way no glue will come off and you can hold it better.