Violin Position

My son's been struggling with keeping his violin up. Every time he tries to correct intonation or play fortessimo, his violin goes down.... His teacher repeatedly remind us that he needs to keep his violin up, but so far we are getting nowhere. I keep reminding him during his practice whenever I am present, but he seems to be very irritated. I understand why. I bud in every second. Then it escalate to an argument. I am so tired.... I told him he needs to come up with something so I don't have to keep telling him. Usually he sits down to practice. That doesn't help either, but his legs get tired standing up for a long time, so he alternate standing and sitting. I thought of something last night and suggested him this morning that he can sit right by our upholstered chair so the scroll of the violin will be just above the highest part of the back of the chair. That way every time his violin droops down it will touch the chair and instantly remind him and since it is not hard object, it doesn't scratch the violin. It seems to be working, thank goodness!!! Hopefully, if he continues with this for awhile, it might correct the problem. We shall see.