You could find one made by Outward Hound for your small dog. But Outward Hound backpacks are crappily designed and poor quality…I probably wouldn’t get one, since you actually need a backpack for real hiking trails, not just in the city. Unless you just want your little dog to have one and will put equipment and supplies in your big dog’s pack. In case you’re interested, though, here’s one: http://myoutwardhound.com/oh05307.html
I got a Canine Equipment one and it is absolutely awesome. The material holds up well to running through trees and getting snagged at by bushes. The long saddlebags help distribute weight evenly along the dog’s back, plus they are removable if your dog wants to take a dip in a river or lake. The chest and 2 belly straps are super padded with adjustable padding. It had reflective linings on it. Lots of separate compartments in the saddle bags (perfect for poopy bags). Oh, and the saddlebags are breathable on the sides that are directly next to the dog’s body.
Needless to say, this is an amazing backpack! I’ve had it for 4 years and it’s stood up to miles of hike trails. Not to mention it is sturdily made. 2 years ago I was hiking on the interior of a mountain in April and the trail turned to complete ice. I had no way to go up besides hanging on to the handle of the backpack and letting my dog PULL me up the hill. It’s amazing.
http://www.rcpets.com/rcpets/index.php/browse/category/id/Pack#main_panel
Ooh, looks like it also comes in red. sharp.
Here’s a pic of my dog wearing it on a hike:
http://inlinethumb53.webshots.com/51508/2896723830096098641S600x600Q85.jpg