Your dog should wear a harness if it pulls on a leash or has upper respiratory problems. (Reference 1) Harnesses also allow more safety when taking your dog out for exercises such as bike-joring or roller-joring. (Reference 2) Even though commercially made harnesses come in various sizes, they may not be the perfect fit for your dog's shape and size. Making your own dog harness will ensure a perfect and comfortable fit for your dog.
Purchase appropriately sized webbing in sufficient quantity and the right hardware for your size dog. Harnesses for small dogs should be made of webbing that is 3/4-inch or 5/8-inch wide. Medium to large dogs should have webbing that is one inch to 1.25-inches wide. Extra large dogs require webbing that is 1.5 inches wide or wider. Your required hardware needs to match the size of the webbing. Your plastic buckle, D-ring and slider all must match the width of your webbing.
Lay webbing over the neck of your dog. Bring the webbing together in front of your dog where its breastbone is. Pin this point, leaving a tail of two inches on either end. Cut the end that is still attached to the roll of webbing. Sew this length of webbing together on your sewing machine with coordinating thread. Overlap the two ends of webbing by two inches and sew together. Reinforce this connection by sewing a box with an "x" in it. This becomes the collar area of the harness.
Loop webbing around the harness and sew where the webbing joins together again. You can also sew the new webbing joint onto the collar area or you can leave the loop free so you can shift this section of harness. Measure how far you want this top section of the harness to extend down your dog's back. Add six inches to this measurement and cut the webbing accordingly. This will become the top connecting portion of the harness.
Slide the D-ring onto the end of the webbing that forms the top connecting portion of the harness. Loop the end of webbing over a new length of webbing, keeping the D-ring at the end of the loop. Sew the end of the loop where it rejoins the webbing that forms the top connecting portion of the harness.
Drape the new length of harness under your dog's belly until the webbing meets again. Add 14 inches to this length and cut the webbing. Slide the webbing out of the loop that is part of the top connecting portion of the harness.
Insert one end of the webbing through the slide. Sew the end of the webbing to the webbing coming out the other side of the slide by sewing a box with an "x" in it. Thread the free end of the webbing through one side the plastic buckle. Unbuckle the plastic buckle. Thread the free end of the webbing back through the slide. Finish by threading the webbing through the other end of the plastic buckle. Connect the end of the webbing to the webbing coming out the other side of the buckle by sewing a box with an "x" in it.
Form a loop around the collar for the bottom portion of the harness. Sew where the webbing joins up again. Pull gently as you wind this webbing down your dog's chest to reach the part of the harness that sits behind his front legs. Form a loop on that end as well. Cut the webbing as needed and sew where the webbing joins up.