Hoisted by my own petard

Homework. Exams. Apparently not as important as re-arranging the furniture in your room and placing your book collection in order of size... Now I know that I am to blame for some of this newly adopted tactic by the son and heir to displace any school-related activity in favour of a more mind-numbing activity.
For 10 years, I have tried with a monumental effort, to get my son to tidy his room. For 10 years, I have also, with an even more monumental effort,tried to get him motivated to do his schoolwork and study.
Now, in a cunning twist of events and with a certain amount of intellectual aplomb, my son has decided to do his homework in his room (ok, he's 15 - we'll go with that) - but first, he has to completely overhaul his room to ensure it's habitability. Unfortunately, this process can take 2 hours - not leaving much time for schoolwork, but leaving an immaculate and ordered room. Now, this new approach towards his pit is, don't get me wrong, refreshing - visitors may use the bathroom and on the way, not mistake his room for a pig breeding centre or an experimental toxin laboratory. When people ask if they can use the bathroom, I glow with pride, I am like the woman from the shampoo ad - I shake my lovely shiney hair in a carefree manner and beam 'Of course, go right ahead, take your time, maybe even 'linger' for a while outside my son's room...'. I fight the urge to give them a camera.
The trouble is he knows I like 'tidy' and 'clean' and that I like his room to be tidy and, because his study time is obviously more important, I am going to have to utter words which I know will stick in my throat;

'Forget your room, come and study.'

Coup de grâce, checkmate, 'hoisted by your own petard', 'stitched up like a kipper' -he will use my words to his advantage for ever more. If only he put as much effort into life skills as he does into out-witting me... His bedroom will once more return to its natural state, while he pretends to work (staring at a school book for 3 hours while really plotting his next move). Once more, when visitors ask to use the bathroom, I'll look plaintively at them and say 'We haven't got one...', it's that or blindfold them while spraying half a can of 'Oust' in front of them as they climb the stairs...