My Siamese cat of 5 years uses his cat litter tray regularly but also urinates on clothes, windowsills, carpet and i caught him urinating in an empty linen basket.
He is a very loved and cared for cat.
We have another siamese cat - a female with whom he adores.
He has only started urinating in the past year in other places as well as his tray which is kept very clean.
Your help in this would be very much appreciated.
First, i recommend that you buy 2 litter boxes. The cats are marking territory. This is common when you have more then 1 cat in the house. Clean the soiled area with natures miricle. This will neutralize the scent. If nothing works you can try valium. Talk to your vet about it. vetcare