I believe it's a case of 'use it or lose it' in terms of intelligence for dogs, as it is for us humans, so I try to keep Penny thinking. Today I came across a link on a German-language blog to a dog toy I haven't seen before. It's called Dog Spinny.
I wrote many months ago about the fascinating toys for dogs available in Europe, but couldn't find anything similar in Australia. (One of the links in that post no longer works, but the fascinating Fun for Dogs still does.)
On YouTube there's a demo of the Dog Spinny. It looks great, though I wouldn't leave a dog to play it alone.(As far as I can work out, most of the European intelligent toys are intended for interactive play between humans and dogs.)
On AOL there were more clips of interesting toys by the same manufacturer, Nina Ottosson.
The problem for me here in Australia is the cost of postage of a heavy wooden toy. So, I was pleased to see that there's a plastic version. I'll contact them and see if it can be posted to Oz.