sorry to hear about the dog, it happened to me a few years back, but i was incharge of my mates whipet, when it pulled of its coller at a gate way and ran onto the road.
its sods law when it happens to your own working dog, and yet you can drive around any estate and see stray dogs running in and out of traffiic unscaved.
anyway i echo other comments that you cant beat having your own pup watching it growup, spot its first rabbit, chase and miss his first rabbit,then chase and catch his first rabbit. its a magic feeling and worth all the hard work.