When I used to work near Whipsnade, many of the locals used to swear that it worked - but the smell of the pellets were worse than anything the cats could have done.
My next door neighbour has tried lion dung pellets.....don't waste your money they didn't work! He has now removed one of the fencing panels that separate our 2 gardens and replaced it with see through netting, the reason being is that my Border Collie barks like mad at cats, and when he is out there and that is a good part of the day, cats won't come anywhere near..........................................I'm thinking of sending a bill for his services, Ha Ha!