please help!

ive found random objects around the house covered in cat pee. from newspapers, to paper bags, to t-shirts, to tissues, and now the bed!

ive got one adult female(fixed), and 2 kittens about 12 weeks old. a boy and a girl. my instincts are telling me its the boy thats the culprit but i can never catch em at it so i dont know who is doing it! i just want it to stop! i really dont want to get dig of him......


does anyone have any suggestions as to what i should do or what may be causing this??