I am looking for a small, lightweight dog backpack for a medium size dog (small-ish collie cross). It is only to carry her poo bags (and her bagged poo when necessary) whilst out running. I am hoping that a Canicrosser or runner will be able to help? She will only be wearing it for a couple of hours max so doesn't need a lot of capacity. It does need to be lightweight, breathable and fairly snug so the contents of the pockets don't bounce around whilst running. Most of the ones I have found online seem much too roomy for our needs and are designed more with all-day hiking in mind. She has quite a deep 'barrel' chest if that makes any difference? Many thanks!