You can try a mist of vinagar, you may have to try this several times to remove all the odor. use a black light ( at night if outside) and cat urine will glow under the light, , for your dryer vent, you will have to either remove and clean it real well. or go to your local home do it yourself store and replace it.. for "strays" i would do 1 of several things. go to your humane soc. and get a trap..or get some nasty "shoo away" stuff made for repeling pets.. this can get costly.. .under decks .. you can try some carcoal.. IE bbq stuff all broken up and sprinkled on the urine.... some janitor supply stores also carry urine removal products, but again be prepaired to spend alot.. so try the vinagar 1st ( 2-3 times) first..