Diy Dog Car Harness . To begin, choose a size of rope that is appropriate for your animal. The first diy dog car seat on our list is from life of posey. 2 in 1 No Pull Dog Harness/ Car Travel/ Walk Combo (Large) Ultimate from www.ultimatedoggear.com.au A small towel won’t do because it doesn’t fit around a big. Diy dog rear lift harness. All dogs need a collar or harness, but you don't have to buy one.