That's good advice, but I'd go one step further: take dog to where there is no rabbits, a park or similar: throw a dummy, rabbit skin covered, put the beam on the dummy, send dog for it. Practice this a lot, then send dog out to end of beam without a dummy being thrown. Dog will be looking for dummy, but then you call it back. Reward with dummy when it gets to you. Let the dog grab hold of the dummy for a moment, then tell it to give, and throw it again, put beam on it and let dog bring it back.
The idea behind this is that the dog comes back to you the moment you tell it to, whether or not i