Seat Cushions are always sliding out.. Grrrrrrrrrrrrrrrr

We carry a roll of industrial grade Velcro. We use it to hold things in place in storage and used some to secure the seat cushions because we had the same issue you have. The industrial grade is wider and has more holding power. I put it on the seat cushions and the opposite piece on the seat and let them sit for a day before putting the cushions back in place.

Problem solved!