I just purchased a cooling bed for Edan to use at agility trials,
http://www.soothsoft.com/cc.html. We purchased the small size but if you have a larger Sheltie you'll want the medium.
Its great because it's just memory foam and water; fill it with water, get the extra air our and seal the opening - one time process. As long as the ambient air temperature is lower the the dog's body temperature it'll feel cool.
I currently have it in our bedroom for him to lay on overnight because its been so warm and we haven't turned on the AC yet.