I've never tried Slime brand, but no liners are completely impenetrable. I go with standard Mr. Tuffies and they hold up to a lot. I have Mr. Tuffies Lite, also and they seem to offer less protection than regular Mr. Tuffies, so I'll stick with the regular, personally.

Also check your tires often, dig chunks of glass, thorns, metal wire, etc from your tire as they can often work their way through the liner if left there.