I agree with
uberglamorous. Dogs bark when they are trying to communicate something. It is important that you understand why your dog is barking.
Our dog had the same problem too and we were all getting pissed at him barking every night. We then found out that our neighbors cat would "visit" us every night.
The question raised by
bigtom59 has importance too. Dogs that are confined for long periods of time without supervision gets bored and will bark as a hobby or to entertain himself. Walk your dog or play with him and make sure he gets enough exercise.
