Little up-date :
I think we are going to succeed ! My husband and I are tackling this issue this week - before he goes back to work. The pathing/hushing does not work - he is immuned to it - We pick him up and put back down. The first time it took an hour or so. The second time, we are down to 45 minutes.

My husban is totally into it and he is as stubborn as my son (who is resisting as if his life depended on it). I see the light...
Thanks for your advices,
M.