Hey congrats on the 12 week old rabbit i love them! My rabbits 12 weeks old cross breed lionhead lop hes gorgeous. Basically my mate took him out for some fuss for about half hour and he lay on her neck really content - when it was time to put him back he had done about 10 droppings in her hair, another 10 in her hood and another 10ish down the sofa hahaha! Funnily enough since then he hasnt done any mess out of his cage. Apparently rabbits like to do there business in the same place. My rabbit now i put his cage in the floor in the kitchen and he hops out and about then goes back in to mess which is really good! Ive heard they pretty much train themselves as they are very clean. Another alternative i heard is that putting some soiled sawdust with a few of his droppings on a tray or something and he should automatically go there. If not like above says just try googleing house train rabbit! Good luck!