we use the diffuser for a bratty cat that also has a weeing issue (clean washing, beds, dog beds, lounges etc) it took about 2-4weeks for it to work fully but after that we only had issues with weeing when DF forgot to clean the trays. we paid $80ish for the diffuser and about $55 per month for refills but we buy from the vet, im sure theres somewhere cheaper that u can find. i no theres some for sale on ebay...

only thing is that u should talk to ur vet about it cos they might have cheaper/other suggestions to resolve the issues.