In the classes I took the trainer taught an "emergency" come. You do not say it all the time. Sometimes we say Rover come! so often that they tend to start to ignore the word.
My emergency recall word is "schnell" something that i wouldn't generally use in everyday speaking.
I adopted this technique with my Collie/Dane, using the command "Now!" in my stern teacher voice! It is actually very effective for those moments when she is distracted by smells and portions of lamb and rice by the skips!
We recently acquired a 3 month Lab/Husky cross, and he has been very responsive as well. Whilst he almost always comes to "He-ere", he sometimes wants to keep playing - but "Now!" seems to be working very well.