Here is a sweater I designed for my boy Max, and even though the yarn is as soft as a cloud and very light, the sweater has lasted him 3 winters! It's true! It has held up nicely even though he did get it quite muddy on three occasions when we went hiking in the snow. I though for sure the sweater would be stretched out and ruined, but after I got home and washed it and lay it out in the shape I wanted--it was "good as new" each time! Now, I would like to point out here that I mostly had my pup wear the sweater on cold days around the house, and outside on days when it was not raining or snowing. Still, I think the garment has held up remarkably well because he is a dog--and for this reason is quite hard on anything he wears, even his leash and harness!
I believe the secret is in the sleeves! You see, doggie sweaters without sleeves (with just holes in the body of the sweater) tend to pull rather hard on the front of the legs, and this results in excessive stress on the knitted fabric. (It is also not very comfortable for the dog to wear!) By adding even short sleeves to the armholes, the sweater is not subjected to this pulling effect and the result is a happier dog, a more comfortable sweater, and a more durable design that has lasted over 3 seasons! This is one of those cases where the construction of the piece substantially enhanced the function and durability of the knitted item. Needless to say, I put sleeves on ALL of my new doggie sweater designs. :)