I've always worked very hard to have decent recalls on my dogs. Having a reliable recall is the cornerstone to having dogs that are able to enjoy off-leash time safely. It takes a lot of work to maintain a reliable recall with any dog, and with some of the more independent breeds, like terriers and hounds, it can take even more work.
Contrary to some beliefs, it -is- very possible to teach your dog a very successful,very reliable recall using a reward-based approach. I am happy to be able to run my dogs off-leash regularly in a number areas in which dogs are permitted to be off-leash, as my dogs much prefer running along a beach or a river to a fenced-in dog park. That being said, regardless of training method, it needs to be known that *any* time you take your dog off-leash in an unfenced area, you are taking a risk. That doesn't apply to just reward-based training, it applies to ALL forms of off-leash training. There is no 100% when it comes to dogs, as they are living, thinking, feeling beings that have their own desires and motivations. So even the best trained dog can fail at some point - whether that dog has been trained with food rewards, tug toys, or shock, the dog always has the choice once off-leash to pursue its own goals. I have seen recalls fail from all of those training methods (and others), most of the time with no repercussions, as the dog does eventually return (like after chasing the deer), but sometimes it only takes once to result in disaster. I don't know how many times I've heard "But he's never done that before" - the problem is you only hear that in the bad news cases. The cases where the dog comes back eventually is often brushed off, and not taken seriously as it should be. So before you decide that off-leash freedom is "the best" option for dogs, think long and hard about how well your dog understands to come when called, how much effort you are willing to put into teaching it, and what types of places you may be able to safely have your dogs off-leash.
So, what does that have to do with whistles? Well, going from two, to three, and now to four dogs, who all enjoy off-leash time together, you eventually need a way to call all of the dogs to you quickly. It gets a bit cumbersome to call them one by one: "Zipper, Kash, Gaci, Shimmer...come!". So to create a nice, crisp, clear recall when I am running several dogs off-leash, I am teaching the dogs that the sound of a whistle chirping means "Come!". I was also interested in how a non-verbal acoustic signal to recall would work compared to their verbal recall. Of all my dogs, Gaci is the one who struggles with recalls the most. This coincides with the fact that she has the highest prey-drive of my bunch and when she is out and about she very easily gets pulled into her own world of smells and animal dens.
I started out by simply chirping the whistle, and then dropping a handful of their supper on the floor, the same way I would teach a dog that a click means treat. I did that many, many times: whistle = food. Once I did that for a few days, then I would blow the whistle, drop some food on the floor, and then take a few steps away from them. When they were done eating they would naturally begin to approach me, so as they were coming I would chirp the whistle again and drop food for them when they got to me. I did this as a group exercise, although I could have done it one by one as well, but since they already have a decent recall, I decided to start it as a group exercise. I will be working them individually (or in pairs) when we start taking it to more distracting environments, but for the indoor work I am comfortable working in groups.
Once I was able to take a few steps away from them, and they were eagerly running to me, I started adding some new understanding to it. When I let them out for a bathroom break, instead of opening the door and calling their names, I am going to use the whistle to get them to come indoors, where they will be met with high-value rewards. I keep one whistle upstairs and one downstairs so that when I get the urge, I will do a "test" and chirp the whistle when the dogs are on a different level or when they aren't paying attention, and reward them when they arrive. I will also know this way who is really gaining understanding of the whistle as a recall cue, and who is not, so I can work more individually with any dog who is struggling.
Today was the first day I took the whistle out into the woods. I took Gaci and Kash down to the river today to let them run and swim and do what they pleased, while I tested their skills with the whistle and practiced some recalls. The key with making them fun and successful is not to over-do it. Also, I make it a point to always send them back out to play as a reward, so that coming when called is not a signal for ending all of their fun. So in the hour that we spent down by the river, I probably only practice five or six recalls, varying the situations from really easy to moderately hard.
Here's the video from their run a couple of days age, with a few of their recalls thrown in. At the 3-minute mark, I whistle them to return and only Kash does. Then I call Gaci verbally, before I realize that she cannot come because her long line got stuck on a root and she couldn't return to me. All in all, I'm very pleased with how quickly they drop what they are doing and come rushing back.
This video is of Zipper and Shimmer practicing in the same place: