If the shingles are brittle, you can spike your jacks right on top. Pull the nails, and fix their holes by slipping a piece of step flashing under the affected tab. Yeah, it's hack, but it keeps 'em dry. Works slick getting off a brittle patch job.
Rope works nice if the job is light enough, and you can rig. Handy on tin.
I usually cats paw top down hook blading to the nearest tab, but I'd much rather blow it apart with a Razor Bar :twisted: