Which GPS tracking collar?

I have a treeing Walker that we use for trailing deer from time to time. She loves it. Problem is, she saw a live deer last week while I was gone hunting and ran off from my camp. Luckily, I found her a couple days later thanks to a guy on here. Been wanting to get a gps collar for a while, but now I'm biting the bullet and doing it. What should I go with? I want something that is going to work in remote, heavily wooded areas. Also would like it to have an app on the phone if that is reasonable. Thanks for any advice

I have been through most of them and the Garmin Astro collar with shock, tone, and vibrate capabilities is the best all round in my opinion. Not familiar with any that have phone apps.

Meant to say Garmin Alpha. The Astro works great but does not have the training features.

For sure the Garmin Alpha. That's what I use on Otis.

If you purely want something to help you find your dog if they run off Whistle is an inexpensive alternative. http://www.whistle.com/ You can take the base station with you if you are travelling. There is an app that shows you where the dog is on a map. It will also send you alerts if the dog leaves the "whistle zone" you have set up.