Leather Martingale Dog Collar (Rio). This beautifully crafted leather martingale collar combines the functionality of a martingale collar, with the design and comfort of what Angel collars are known for. Perfect for training or anti-pulling, this collar offers a more humane alternative to choke collars. Made of 100% genuine harness and cowhide leather. Available in 8 sizes and 4 colors. Now with stainless steel hardware. Leather Preserving Products Rio Martingale collars are sized leather tip to tip (not including chain links). There are 2 measurements: Collar completely fastened and collar fully extended. If you want the collar to adjust exactly at the rings, select 1 size down from your dog's neck size. If you want the collar to squeeze the dog's neck when pulled, select 2-3 sizes down from your dog's neck size.