A guy I know used a bucket of water and a rolled up newspaper...
He called the cat over...encouraging it with a treat, grabbed the cat by the scruff of the neck.. shoved it's head in the bucket of water, then bashed it over the head with the rolled up newspaper... then repeated the process several times...
He says he's had no problems since...the cat's petrified to come anywhere near his garden now.

I of course do not agree with this cruel and barbaric procedure... just thought I'd share this with y'all.

I know first hand the problems with pets fouling my lawns, and agree it's annoying.. but the Lion poo idea sounds the best to me.. if it's still available from Longleat.