From Grange...My father traced his dog's outline then attached the cut-out to two spring hinges (attached at the front and back feet of the cut-out). He then attached the spring hinges to a simple 2x4 "frame" and used a hook from the otherside of the frame to hold down the cut-out by an eyelet attached to by its head. The hook is attatched to a string so when he brings his dog into view either he or someone else will pull the string and the backing dog will pop up. This is a much more ecomonical way than the a $500 electronic backing dog though you do lose some convenience.
From Fishvik...Just get a picture of your dog on point and then grid it.(Break up the photo into squares, 1/8 or 1/4 inch squares should do ) Then measure your dog in inches and compare it to the photo. If your dog measures 36 inches from front to rear and on the photo it takes up 6- 1/4 squares from front to back thenEach 1/4 square on the photo represents 6 inches in real life. So layout a six inch squares size grid on plywood and copy your dogs silloutte from the photo onto the plywood.
http://www.gundogforum.com/forum/viewtopic.php?f=89&t=17058&start=0&hilit=backing+silhouette