Citronella collar?

Question
Hi there! We have a 7-month aussie that enjoys chasing, cornering & nipping at our cat. On an aside, we have been taking her to obedience classes, during which she has done well. We have consulted with the behaviorist, who first suggested interrupting the behaviour with a strong verbal "ah-ah", immediately followed by spray bottle squirts. That only seems to work the very odd time. So, our behaviorist has suggested introducing a remote-controlled citronella collar, one that provides us with both a positive reinforcement (a audible tone, to which we would provide her with positive feedback & treats), as well as a strong distraction/interruption (the citronella spray) the moment she starts to go after the cat. I do not mind investing the money in this if it will help, but I am wondering if you could give me your thoughts on this approach & whether it is safe. The behaviorist said that we don't want to create fear in our Aussie so she said to see if she can be redirected following the citronella spray & receive treats within two minutes. Hope this makes sense. We would really like to try & find ways to ease the relationship between our pets. Thank you!!!

Answer
An old stock dog trainer once told me that it was easier to teach an Aussie not to herd cats, horses, kids, etc. if you first allowed the dog to herd sheep or cattle, so that they would know what they could do, before they had to learn what they couldn't do.
I actually did take my Aussie to a couple of fun herding instinct days, so that she could do just that, and it has worked rather well.  Prior to that, I taught her to "leave it" "stay" and "come" so that she would have a cue that gave me a shut off switch for the cats, horses and kids lol.
However, I do not think that it's a bad thing to use a citronella collar under the supervision of a positive trainer who is well versed in its use and in the principles of operant conditioning.
Your timing must be exquisite, though - the spray should hit the dog just as she is *thinking* about going after the cat - right in that first millisecond of flight.  Once the predatory drive is really engaged, you are way too late.  Also, the reward should come within a second, not minutes, of the right behavior.
Also, I would create a "safe zone" for the cat - somewhere she can go where the dog cannot follow.