I generally have a mid-class height dog (not first!), so I try to locate the leash runner before I get my dog out, or at the very least when s/he is walking back from having delivered a leash to the finish line (assuming s/he's not holding it for the person on course). I realize this isn't always possible, given various ring layouts, distance to crates, etc. But I try. If it doesn't work, it's usually only another second or two to get the slip lead end up and over my dog's head. Way faster than fastening the harness! (which is kinda my point...)
diane