Agree with everything Pat said.

On Sat, 9 Jul 2011 11:16:23 EDT, "Pat" wrote:

corrosion on the prongs

You might try some silicone grease

Could I cause serious problems by not submersing the lights?

The fixture probably relies on being submersed for proper cooling.

Is copper truly toxic to fish?

Yes, however it depends on the chemistry of your water whether the copper
will dissolve into the water.

IIRC, I believe the worry is when the water has a pH of 7 or less, but one
might want to google this for sure? Most fish ponds are usually higher...
check your KH/buffering, as that can make the pH change AM to PM. You need
buffering to keep your pH somewhat stable. ~ jan

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Zone 7a, SE Washington State
Ponds: www.jjspond.us