I've got a friend with the same problem... he sprinkles black pepper in a fairly wide swath around his plants (other suggestions are cayenne, dry mustard powder or coffee grounds)... cats don't like the smell and will (apparently) stay away... but it would need to be a WIDE swath so they don't jump over it... In the case of the pepper, I would think you'd have to re-sprinkle after a rain. Don't know if coffee grounds work (he doesn't use them) but I would try THEM because they wouldn't be affected by rainfall. Ask your local coffee shop for a donation of their used coffee grounds... you could even provide them with a 5 gallon bucket to collect them in... at worst, you'd have to remove coffee filters from the pile before scattering them on the ground...
Good luck - MY cat only likes to sleep under them and then only when they're in flower...