Or you weld a post to a section of diamond plate large enough to hold 45 pound plates, and weld a lip on the front, with a loop to attach chains/ropes to.
GET A free used old tire from a tire place, they have many they are throwing away and the dude thought I was a football coach or something but get an old tire and then get some plywood so you can BARELY squeze the plywood into the middle of the tire so the wood stays in the tire so you can put weight plates on top. Then drill a hole near the side of the tire so you can run a rope through it and then tie the rope to the weight belt.
Thats how I did mine and it works fine
another description is given at the end of the article 'Drag Your Butt into Shape" a www.t-mag.com
The sled that Spatts mentioned is much better than the tire sled I made but if you cant afford it then the tire is ok.