Seams! That seems to be where most leaks
happen. Both the leaks
on my Boston Whaler were by a glued section and one of them has started leaking again.
But according to the instructions for my hypalon inflatable
one is supposed to rough the surface where the patch is supposed to go, and the bottom side of the patch.
Then brush glue on both of those surfaces and let it dry until tacky to the touch. Then put the patch on the surface and press hard. It helps too if one has a tire patch roller to finish off the pressure.
If a leak is next to glued-on tab, (e.g. handle) sometimes one has to lift
the tab enough to add a patch and re-glue the tab over the patch. In that case the patch needs to have beveled edges.