How can I fix my Citroën Picasso gear stick?

I have a 53 plate Picasso and have had problems with my gear stick, first it came off so had it welded back on, then my gears were stiff so my husband oiled gear cables which sorted that problem but now when I put it in reverse the stick pops out where the ball is and I have to get hubby to pop it back in so I can use my gears. Is there an easy fix for this as I'm not using car at the minute because it's too unreliable especially with having children and don't want to get stranded!!