I have the same problem, I plan to buy the Garmin Swim watch, see http://sites.garmin.com/swim/ It has some good reviews, e.g. DCrainmaker, see http://www.dcrainmaker.com/2012/06/garmin-swim-watch-in-depth-review.html

Through an accelerometer and clever software, it detects styles of swimming, measures laps, strokes, stroke rates and exercise time. The instruments is targeted for swimming in pools (no GPS).
Based on the site and the review, it seems like they have thought about the usage.