How tear proof? For a tear proof cover which doesn't tear other things, perhaps wrap a carrier bag over the seat and secure with sellotape at the seatpost, then paper mache:
...wait till it dries, cut it open down the middle, reassemble and repair elsewhere using wallpaper glue or epoxy, and layers of newspaper strips, smooth it down with sandpaper, and paint. Make sure to make holes, so you can secure it with zipties.
An easier solution is to use at least two cheapo covers. One "Waterproof" cover is never waterproof enough. Like the two cheapo rucksack covers over my ebike battery.