Great article -- 'The Disappearing Sit'. A lot of people post here every year asking about why their dog has stopped responding to commands he or she knew. Here are the likely reasons and what to do! Note yet again that the issue is almost certainly never the one old style trainers have so incorrectly taught people to assume --'dominance' or willful misbehaviour.

http://www.dogloversdigest.com/2011/...appearing-sit/