Something that I have used, with considerable effectiveness, are high output quartz lamps tied to motion sensor controls.

Having worked around commercial properties for years, I HATE alarm systems. 90% of the time when they go off, they shouldn't, but at least 30% of the time when they SHOULD go off, they don't. I nearly got shot by a rookie cop one night, doing some heavy duty maintenance on a restaurant (I was a plumber, before pools). I was working at 3am -- when I could turn ALL the water off -- and had keys and codes, but the manager had forgotten that outside entrance and boiler room had a SEPARATE alarm.

Odds are, if you put a sensitive alarm system out there, you'll be out there 3 nights a week discovering all the critters living in your neighborhood.

The nice thing about lights is that they say to any intruders, YOU HAVE BEEN DETECTED!, without waking the whole neighborhood, if the 'intruder' is just a cat or raccoon. If you use a few 500W quartz lamps AND some hunting cameras, you'll get nice hi-res color shots of your intruders. And, with a good pair of binocs, you should be able to see what's out there without having to go all the way to the pool.

One observation: I've had people ask, shouldn't we just leave the lights on, all the time? The answer is no -- not only does it waste electricity, always-on lighting doesn't communicate to intruders that they have been observed.