About a year ago I bought a Sure Fit slipcover for my sofa and love seat in my living room, our living room seating was pretty beat up and needed a lift. At first it seemed like the slipcover was staying in place, but after a while it started to sag and bunch up. This might of had something to do with my 3 year old jumping around on the furniture. I started to think about how I could fix this problem without having to buy new slipcovers, or make new slipcovers. I finally came up with attaching Velcro to the sofas and the slipcovers to keep them in place.
If you are looking for decently priced try Slipcovers on Amazon. Make sure you get Velcro that is made for fabric, otherwise it will not stick.
These after pictures were taken a few days after finishing this project, it seems to be taking all the abuse that a 3 year old can dish out.