i use both the LaCrosse repair kit and Shoe Goo. The LaCrosse kit is smaller that a pack of cigarettes and about as heavy. Contains a patch that you pull off the backing and can slap on. Works best on a flat surface, but gives a immediate seal. Eas to carry in the field. Once you dry it back at home or camp, cover the edges with the LaCrosse urethane cement from the kit or some shoe goo. I like the LaCrosse boots that buckle on the side (compensates for my high instep that keeps my foot from going easily into or out of boots), but this style of boots have a weak point in that the area around the front of your ankle abrades and gets cut up and leaks. I will take the boots and put a layer of shoe goo or urethane their and just replace it periodically.
The shoo goo works if the tear is not where the boot flexes.. I have a pair of RedHead Bone Dry.. both boots cracked where they flex at the back of the toes.. I have shoo gooed the heck out of those boots.. several times.. they keep cracking in the same place..