In article ,
John Doe wrote:

Another very strong deterrent, used responsibly of course.

Not suggesting there are many (if any) good uses, just that it
makes a serious impression.

I would worry about the eyes with compressed air. A simple spray bottle
(loaded with water, or maybe sulfuric acid) is probably safer.

I once had a squirt gun with bits of plastic in it that made it rattle
when shaken. After a couple of, ummm, incidents, it turned out that I
just had to shake it once to get the cat's attention, no shots required

Yeah, sulfuric acid might be a bit harsh...