In your case, I would recommend using a distraction before using Come. Dogs with absolute bombproof recalls could perhaps be called off a bike or a rabbit with "Come". But most dogs need a distraction to pry their mind off the situation. In an ideal situation, say your pup is off-lead and she has just begun to chase the bicycle. Throw a can of pennies in her direction and in the split second that she pauses at the noise, command a "Come". The problem, however, is that we generally don't have quick enough reflexes. You could also use a VOG "NO!" or call her name, but I doubt the dog would even flick its head in your direction with these. Some people use electronic collars (both shock and citronella) to pause the dog and gain that bit of precious time to call the dog back. I don't have experience with either so I can't vouch or criticize them when used in this manner. However, I do agree with the others. Dogs who don't have very very reliable recalls generally shouldn't be let off-lead, especially where there are dangers like bikes and bunnies.