With three dogs weighing 70, 80 and 90 lbs we have found that the 4-6' leather leashes work best when walking. We keep the dogs on a loose heel with a slack leash.
In the campsite we use 15' training leads clipped to the step with a carabiner, or to the picnic table if one is available. When we had just two dogs we tried the plastic coated cables like the one shown in a previous post in the campsite, but after a few trips they became quite distorted and hard to roll up for travel. The fabric training leads work best for us in the campsite.