The velcro that I used has the sticky back that I put on the Dulcimer and on the strap. I did also sew it to the strap. But if you can't sew it I would think that a little hot glue might work or perhaps contact cement. I also put a buckle in my strap so I dont have to unfasten the Velcro each time, this also makes the strap adjustable.
Hope this helps