Update 4/8/11: I found an improved wireless pool sensor at the local Home improvement store called Acu-Rite model 00617. The design seems superior to this leaky one. The Acu-Rite has 5 screws that hold the top seal, and the base unit shows a temp graph for the last few hours and days, plus it shows the wireless signal strength. And it costs half the price of this one! The Acu-Rate is also made in China so let's hope it lasts longer than this one did.
I'm on the 3rd pool sensor. I took steps to protect the second unit by putting silicone sealant around the seam next to the rubber ring. This lasted longer, almost a year, but it still developed a leak right onto the circuit board and was also destroyed! So I finally discovered that the leak also appears to be coming from the seam at the top where the Antenna's grey rubber cover meets the plastic enclosure. Other reviewers are also having the same leak problems if you check out the other reviews on this product. I keep replacing the sensor because so far I haven't been able to find a nicer pool temperature sensor. The manufacturer, Minder Research Inc. is apparently aware of the leaky design problem: the warranty paper says "All RS888 transmitters are 100% pressure tested and are not guaranteed if it stops operating due to water damage."