Guys I am a hunt tester, but I'm planning to try some derbies with a couple of my pups next spring. I've been working this winter on long marks and long Blinds with some of the older dogs. I use a sport dog whistle. Of course there are variables that have an impact on the dog's ability to hear my whistle, but once they get 300-350 yards out, I'm having a lot of trouble stopping the dog. It is really frustrating when I get them stopped and give a cast...dog dogs back and I have trouble getting them to stop again. These dogs stop abruptly on the whistle. I don't have any problems until I try and run 300+ yard blinds. Every dog I'm running these with have had slipped whistles on the same day. I'm convinced they are not hearing the whistle- especially if in running water. What whistle is popular among trialers?