Whenever he or she has finished eating or is starting to sniff around, take him outside to a spot and wait till he does his business. Then praise him. Depending on the dog, this might take a while.
Oh and ignore any mishapses. Just reward the good behaviour (I got our previous alsation to call me when she needed to go outside in about a a week and a half after we got her).
ooh thanx 4 the tip!