waterproof 6x6x6 canvas tarp for dog shelter

I have small dogs who HATE the rain. They won't get off the porch to go if it is raining. I found a 6x6x6 kennel for them. Now I am looking for something waterproof that I can put over and around it. I tried the blue (inexpensive) tarps and they were just beat/shredded by the wind and caved in when some water gathered on it. (The squares are much smaller now so no big weight will gather.) Not sure if I need grommets for anchoring or not. Fixed income, so looking for more for less $$. Thank U