dog weeing on couch at night only

Question
We have 2 male boxers, a 2yr old and a 6mth old, the 6mth old has started to wee on the couch at night despite the fact that we toilet him before bed and let him out before sunrise for another wee. Can you please help?

Answer
If the puppy was previously house trained, and has suddenly started this behavior, the first thing to do is take him to the veterinarian to rule out a urinary tract infection.  Another possibility in a dog this age that was previously house trained, but is still intact, is that he has started urine-marking.  If that's the case, neutering may help.