Here's a quick video of Bosley coming when called quite reliably when he least expected it. He retreated to relax in the shade under a tree only to remember how FUN it is to come running to me when called!!
Don't forget!- Your recalls need to be well trained in low distracting environments first to build the foundation of the behavior linked with the desired cue. Is your dog's tail wagging when they get to you!? It should be fun for them to WANT to come to you!