You mentioned the real key word there...
PETS.
Get a new standard spa cover, and treat the pet. Stop treating the spa cover. Either that or put some kind of barrier around the jacuzzi so the dogs won't eat it!
I've seen it a million times and the only cure is some kind of discipline thing or maybe spraying the cover with skunk doo.... OR, eliminating access to the jacuzzi area from pets.
While I'm at it, I'll get cheezy and plug
http://usaspacovers.com
Your real answer lies with the dog's teeth!
(just my opinion, don't shoot me!)