Over a week ago I put in the motion-activated device which emits a high-pitched sound (higher than we humans can hear) which is supposed to deter cats. First, it startles them when they set off the motion-detector (which also uses their body heat to sense them.)   I was pretty skeptical that this would work but I haven't seen the particular nuisance cat near my pond since I put up the device.  It's green and fits right in with the ivy around the pond. 

I chose this device over the Scarecrow motion-activated water sprinkler cat-deterrent because I wanted something I could use all year round. Plus, I didn't want to risk leaving the hose turned on all the time because it leaks very slightly at the faucet. That would have been a waste of water until I get the faucet fixed. 

Will keep you posted on how well it seems to be working.   M.J.