Add a piece of material sufficiently long as to fit beneath a seat cushion. The length of the arm cover should be so long as to be able to fit behind a seat back cushion.
I'm thinking you might be able to put a piece of the rubber backing material that holds rugs in place. You can purchase it in a roll or rug size. Here's an Amazon link to take a look at:
Add a piece of material sufficiently long as to fit beneath a seat cushion. The length of the arm cover should be so long as to be able to fit behind a seat back cushion.
I'm thinking you might be able to put a piece of the rubber backing material that holds rugs in place. You can purchase it in a roll or rug size. Here's an Amazon link to take a look at:
https://www.amazon.com/s/?ie=UTF8&keywords=rug+gripper&index=aps&tag=googhydr-20&hvadid=318464364129&hvpos=1t1&hvnetw=g&hvrand=14924197777387791437&hvpone=&hvptwo=&hvqmt=e&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9012214&hvtargid=kwd-132309200&ref=pd_sl_3kaqx52cfk_e
Heavy duty velcro strips