Behavior training - Negative Reinforcement

We have a 6 month old Female JRT and we are trying to train her. We use praise, petting, and treats for positive re-inforcement. We like to use Time-out for negative reinforcement but my wife has a difficult time in catching the dog to put her in "time-out". The dog thinks we want to play when we do this and that makes it ineffective. What other methods are available when correcting problem behaviours.
We obviously don't want to hit the dog etc.

Thanks,
GG