I agree with Beane, instead of banning dogs from certain areas, penalising those of us who do pick up, councils should concentrate on prosecuting the offenders. Get a few hefty fines reported in the local papers and people might just remember to put a bag in their pocket.
However, it can be amusing to watch the antics of people 'pretending' to pick up because someone is watching. I've even seen a woman take a bag out and bend over the poo but not actually pick up! What's that all about?