Watching your working dog's attention focus on something other than the task you spent many hours of training for can be one of the most frustrating experiences in the field. Very little attention is spent on distraction training when in a team environment, instead it is left up to the handler to perform this training independently as it is unique to each dog.
If your dog requires some additional distraction training follow some steps to get your dog's focus back. In this discussion I will use chasing a squirrel as an example of a distraction but a distraction can be anything that draws the dogs attention away from its job such as a bird, a cross track, loud car traffic, a body of water, or the dreaded housecat Mr. Kitty. While looking at the squirrel distraction momentarily is acceptable being a distracted by a squirrel to the point it forgets its job, or worse chasing a squirrel, is not.
First we need to understand the dog's proximity alert distance, when the dog's attention focuses on the squirrel longer than a momentary glance but before it chases the squirrel make note of the distance between the squirrel and the dog. This distance is your dogs proximity distance when it alerts and is the starting point for distraction training distances, for some dogs it can be a few feet and for others it can be many yards.
As part of the distraction training the handler will need a reward system as chosen by the dog. The reward may be a toy or it may be food, but this is to be what the dog selects not what the handler thinks is best. The handler will also need to have trained the dog to understand positive commands and also negative commands, for example a positive command can be a 'good boy' using a high pitched tone in your voice whereas a negative command can be a lower pitched 'NAAAH' as if scolding a small child.
Initially Distraction training is to be done as single focus session(s) and is not to be included as part of other training, after three or four distraction training sessions it can be incorporated as part of the regular work the dog is required to do, if required.
For your first distraction training session transport your dog as normal to an area known for squirrel activity. Leash the dog on a long line and stay just outside your dog's proximity alert distance, pay attention to your dog and gradually move the dog closer to the squirrels to just within its proximity alert distance but not so close it chases the squirrel. Timing is important here as the dog needs make a connection between the reward system and the unwanted act of alerting on the squirrel. As soon as your dog alerts on the squirrel the negative command (NAAAH) is given with a slight tug on the lead, the dog will immediately re-focus attention on the handler and at this time the handler gives both the reward (food OR toy) to the dog and positive verbal praise (good boy). Do this three times for each session, end each session on a good action by the dog. Repeat each subsequent session slightly closer to the squirrels until the dog understands it is not to chase the squirrel. This process should only take three or so sessions before the dog understands its job.
Finally, the dog will not be able to differentiate between chasing a squirrel while on a walk and chasing a squirrel while doings its job, as such at all times the dog is not allowed to chase a squirrel. If the dog shares a house with other family members this rule must be agreed upon by all members of the household.