Advice taken from my Cats Protection site:-
Almost daily we are asked to bring in cats just because they have a wee problem or spray. Very often this can be resolved with a little time and patience. I am amazed when I ask have you a litter tray and am told no, often a litter tray provided - problem solved. If you know which cat is weeing or spraying
it is wise to have the cat checked out by a vet in the first instance to ensure there are no underlying medical problems. CP advise always provide a litter tray irrespective of your cats age even if they are allowed out, if you keep an eye on what your cat is passing, you can spot many problems, e.g. cystitis is very common in cats and needs urgent Veterinary treatment. It is shown up if the cat uses the tray frequently and/or passes blood, something you would never know if you didn’t have a tray. We think the covered litter trays are best and you can even get them in most colours to match your decor. We find that the wood pellets are excellent there is no smell of urine whatsoever and if there was then the cat could need to see the vet as it may have a problem. Another problem seems to be when folks have only one litter and a number of cats. Some cats do not like to wee and poo in the same tray so sometimes it is necessary to provide 2 trays to alleviate any problems, ideally one litter tray per cat is the best option in multi cat households. To remove the smell of the urine and hopefully stop a recurrence we suggest you clean the area thoroughly with a solution of hot water and a enzymatic soap powder, allow to dry then wipe everywhere down with a spirit brandy, gin, whisky, rum (I did purchase some rum in France once and it was so horrid I used that on the carpet and it worked very well) and if that is too painful surgical spirit. Once all traces of urine are removed you could put a little dried cat food down or try Feliway spray from the vets, used daily for a time can be a benefit, there is a Feliway ‘plug in’ however I have found it as much use as a chocolate teapot. No doubt some people must have had some success as been on the market for a while now. My own cat Jeannie used to spray everywhere, up wall, on the curtains, this behaviour stopped within in a very short time after I started to spray with Feliway, only very occasionally now does she have a relapse, it is quickly solved with spirit and a few sprays of the Feliway.
Also see www.ssscat.com. However as advised a vet check is a necessary essential initially.