I had several rugs similar to this one that I wanted to use to test Martha's idea.
For this project I used a tube of acrylic latex caulk and a caulk gun, both of which I already had on hand.
Flip the rug over to the back and apply thin lines of caulk every 6 inches or so. My caulking technique is a little lacking as evidenced by the squiggly lines, but that should just give the rug a little more "grip"!
Let the caulk dry thoroughly before turning the rug back over to use.
After the caulk is dry the latex lines will grip the floor and keep the rug from slipping. It should eliminate the need for buying these expensive and troublesome pads to put under every small rug. In my opinion, the caulk should only be used on rugs that are not the washable kind. I haven't tried it, but I don't think the caulk would stay adhered to the rug during washing.