Am working through force fetch with a 10 month old female. She's got the concept down great, lunges for the bumper when I say fetch and is a very willing student but promptly works the bumper around to hold by the end. I don't dare have a rope tied to it or she'll hold the rope, only use a plain bumper so we don't have that issue too. We've been working daily for 3 weeks on proper mouth placement and she continues to do it. If I remove the bumper and put it back in properly she'll hold by the middle as long as I ask. Should I be concerned? Just continue gritting it out with her? Suggestions?