As a last resort, plain old white vinegar in a spray bottle works wonders on anything you need to teach a cat to get away from. Also does great in a water gun (my Mom used a super-soaker on the neighborbood tom cat who kept attacking our old girl). The downside is that you have to smell it too,
though outside it isn't so bad. And soaking something in 1/2 vinegar 1/2 water for a day neutralizes cat pee smell. Then another day in 1/2 mouth wash 1/2 water takes care of the vinegar.
I cannot live without my cats and during college developed bad allergies while away from their constant company. Due to that and other allergies to everything green & growing as well as dust made me start allergy shots to make the sinus headaches go away. The shots have worked well enough that I have a pair of Bengals now, a breed I do well with compared to many cats. Though the cats get a bath every 4-6 weeks and that also helps.