I tend to agree with LagrangeDave, give him an escape route. And he'll leave on his own. Alternatively, a load of birdshot would take the head off, without ruining the coping or killing a neighbor.
And the lesson I take away from this thread is: don't let the pool get all green and nasty. Winterize it, and pull a cover over it. Unless you are going to drop some crappie and catfish in there, and let it go natural.
How about a teter totter made of a 2x6 that feeds into a bucket ? Bait it up so he can crawl past the pivot point and then he will slide down the board and into the bucket. Put some lard on it so as soon as he crosses the pivot he will slide into the bucket.
Bleach jug with a small treble hook attached to a 10 inch leader. Small piece of beef or deer meat. He will swallow it and you will see your jug bobbing like a cork. Get the grease ready.