I originally had a few Platypus 1L bottles, and a few 1-2L conventional bladders with hoses that I used simply because they were available. At one point I had them carrying Nalgene bottles, because they are indestructable. I figured in a pinch I could use them as well, if I ever needed to drink. It definitely is easier to balance their packs, and as we walk, I use my own bladder/valve to fill bowls on the go -- that way, they stay balanced, and it lets them use energy so when I sleep, they sleep! The Platypus bottles worked fine, but they didn't flex as much when full, and I had one puncture on me. I don't always fill the bladders full, but they have notches that I can measure with to keep it balanced.
I actually purchased a Hydrapak Trek Kit 3L to test, from Massdrop, due to the fact that it came with a multi-attachment cap and a silicone squeeze valve. I use this for quick filling dog bowls from my bladder, squirting the dogs to be an ass, etc -- it spits water, and I've found it really useful for being a slightly heavier/bulky water delivery. I decided to pick up a few of the Hydrapak Seeker 2L bladders because they are identical to the Trek bladder. I could swap the caps if need be, hang them the same, etc. They also are shaped nice for my dogs packs, imo, and I find they are malleable. My dogs carry the weight of the 2x2L really well, and it lets them work on the trail. The bladder style, I feel, hugs their bodies more, are longer due to the tube-shape, and hopefully more comfortable for them to carry. They've held up to being beat around by the dogs, and every day use here at home to fill the water bowls. I was personally happier once I moved to this setup, the dogs don't seem to notice!
Both dogs are Shepard-Husky mixes, 2 year olds, at 60lbs each. They're fit and strong, and very prey driven. I can't really let them off of a leash, unfortunately, because, while they listen to commands at home, as soon as they are on the trail they are too excited. After a few miles they pull a little bit less, and relax a little, but I don't trust them not to go diving after everything that moves -- and we hike around Copperheads / Rattlesnakes, often.
Both have identical leashes, that have a "traffic handle" on them. I hook these to the backs of their harnesses and walk them using a carabiner to attach the two traffic handles together, creating a Y. I want the option to separate the two, so this works best for me. Both dogs tend to run forward, stop to smell, run forward, etc. Having them attached together like this makes it to where they pull one another if they stop, so I save energy, and they typically like to be near one another anyway. This would likely help with your dogs. I try to pay attention to when they've used the restroom last, as it can be a bit awkward to have them attached like this and take a dump! I also keep a 'biner on each leash end at my hand, so that I can quickly clip them to my pack/belt, around a tree, or around my waste/leg in case I need to go hands free. This comes into play later, as well, when at camp (or at pubs that allow dogs, haha). The dogs also carry their own Gentle-Leads, in case they are out of control, so they will relax simply by having those on (but I rarely ever need to use these -- last time I did, there was 2 inches of solid ice covering the rocks we were walking on, and I used it so they didn't pull me off of the side to my death, ahha)
When at camp, I typically will tie the dogs off to a tree, and setup shop. I have them each carry 1 part of a 2 part set of Hammock straps - the kind with the multiple loops sewn in. This way, I can give them a bit of space to explore at camp, shorten up the length or daisy-chain them if need be, and not have to worry about them pulling or eating quickly through thick nylon-web-straps. They carry them, so no extra weight penalty for me, and they work as a leash if I need it.
I've not used the stretchy-leads with the dogs, but I doubt I will, either. I'd rather rely on my tried and true nylon-webbing. I can provide you a gear list of what I have, links, or the like, too, if you want. Sorry for the wall of text -- I figured details might be better!
Hope this helps!