Remove the rod and slide off all the curtain rings. Remove the curtains from the rings.
Fold the curtains and set them aside. Go outdoors with your rod, rings and a can of spray adhesive.
Shake the can of adhesive and remove the cover from the can. Aim the nozzle at one end of the rod, holding it about 6 to 8 inches away.
Spray the rod with the adhesive, moving the can in an up-and-down motion. Turn the rod slowly so all sides are coated. Work your way down to the other end of the rod to completely cover it, then lean it against a building to allow the adhesive to set.
Hang the rings from Christmas tree ornament hooks on a clothesline or porch railing to suspend them so that they are being touched as little as possible. Spray each individual ring generously with adhesive. Allow them to dry.
Bring the rod and rings back indoors. Replace the curtains on the rings and the rod over the window. The coating of glue will remain mildly tacky, adding just enough friction to prevent the curtains from straying on their own, but not enough to prevent you from opening and closing them as you desire. The tackiness will also prevent the fabric from sliding on the rings.
Re-spray your rod and rings occasionally when you wash your curtains. With opening and closing the curtains, the adhesive can wear off eventually.