I had the same issue, gear down and locked + spoilers out = Gear horn. Luckily I was on downwind, and I didn't have to listen to the horn blaring away for very long. The guys on the ground could hear it in the background as I made my landing position calls on the radio, and they kept giving me check my gear warnings over the radio.

Now, there is one panel mounted fuse on my panel, and it's for the gear horn. If one of those proximity switches falls off again in flight I can unscrew the cap, pull the fuse, and make it stop.

I thought the panel mounted fuse was better than a switch, in that it was less likely to be turned off (and left off) by mistake.

SF