Nicola you can buy things that shoot dummy's out for dogs to retrieve giving a bang like a gun.. I'm not suer where you can get them but I'm sure if I have a hunt Ill find out. that way the bang is followed by the reward.. the retrieve.. I'm off to have a hunt...
they are quite expensive heres one link..
http://www.scottcountry.co.uk/products_detail.asp?productID=1605