finding tom cat spray or urine

hello i was just wondering how do you find the source of where a cat sprayed or urinated? in a portion of my house (STOrage room) there is this odour but ive cleaned everywhere and i cant find the source! Any tips?

Ultra-violet light. They sell little ones, just for that purpose.

ok thanks, I have desperatly tried to purchase it off the site you gave me however they wont send it to me aparently the area that I live in they are unable to ship here? I am in Canada, it doesnt make sense!

Anywhere else i can purchase it? It sounds to good to be true..

Any other place that sells similar product??

call around to your local pet stores, many should carry it.