Coming when called is
so super important. I am still working with Jackson continually. He used to be off leash a lot more, once he turned 1 years old, he became a lot less reliable. We live on 3 acres with no fence. He has gotten out a few times when a door has been left open (grrrr... stepdad's doing!) He doesn't typically dart, he just kinda walks out like "oh, cool, a door is open" and goes exploring, lol. The last 3 times he's gotten out, he's come right back to me so I think our training has been working. However, for the last year, he hasn't really been allowed off leash at ALL outside of a fence, only the 50 foot line.
I try to use a REALLY rewarding treat like hot dog, chicken, steak, etc when practicing coming when called. I bought a 50foot training lead (Petsmart has these for around $10-$12) and I let him go all the way out 50 feet and then call him to me... so it's almost like he's off leash, but IF he happened to run off, he's still safe at the end of that 50 feet. I also found he responds better to "here" than "come". I don't know why. So you can try different words and phrases.
Also, I read once on here you should have ONE command that's an odd word not used in daily convo, like "Jackpot!" or something that means it's *really* important to come. Train it over and over but once learned, don't overuse it. A word that means he really MUST come.
I'm lucky that my dad has a big fenced in yard and we have a nice dog park. Both are nice places to practice recall. I always keep a few treats in my pocket at the dog park and will randomly say "Jackson, here!" and he responds 90% of the time now at the dog park (with lots of distractions). It's been a nice place to incorporate training.
Basically: Practice, practice, practice! Don't use the word "come" or "here" if you know they are NOT going to come. Set them up for exercise. If you overuse any word, they become 'immune' to it and don't really understand the meaning behind the word. If you keep saying "Come!" and they're not coming... that word is worthless. ONLY say 'come!' when you know they are going to, or after they do.
Here's a good article:
Dog Emergency Recall Command