So, our dogs like to "travel" the property - all 199 ares and then some. We live on a farm in the middle of nowhere so it's not really a concern. They almost always return on their own. The few times they didn't were times when they were testing and learning the limits of their territory (they're only just over a year old). We have GPS trackers for them as well so we can see exactly where they are, within about 10 meters at any time and up to several kms away, depending on the terrain. 

The next thing we want to try is a way to communicate to them when they are too far away to hear our voices. We've been training and working with them since we got them just over a year ago. They're very smart and obedient (most of the time ) so we're going to try attaching 2-way radios to their collars so we can talk to them and relay commands over long distances. I'm curious to see how or if they will respond. Fingers crossed they will come when called through the radio.  

Something like this, I think will do the trick. 

https://www.amazon.ca/Motorola-T100TP-Talkabout-Radio-3-Pack/dp/B01DM7AEF8/ref=sr_1_8?ie=UTF8&qid=1536936663&sr=8-8&keywords=2+way+radios