I just posted this in a previous thread, so I'll just copy/paste:
Coming when called is sooo super important and probably one of the hardest things to teach, to a terrier anyways. That's what I've found. It all depends individually on each dog but terriers are known to be harder to off leash train because of their instincts.
I am still working with Jackson continually. He used to be off leash a lot more, but once he turned 1 years old, he became a lot less reliable because I never
formally taught a solid recall. 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. He used to just stay close to my moms dog so I never taught him officially how to be off leash, but once she died, no longer.
I try to use a REALLY rewarding treat like hot dog, cheese, 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.
I'm lucky that my dad has a big fenced in yard and we also 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 REALLY well most of the time now at the dog park (with lots of distractions). It's been a nice place to incorporate training. As well as our agility class.
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 success. 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
This Youtube account has amazing videos and she is making a whole series about recall and coming when called. She's got around 10 videos right now of games you can play.
YouTube - pamelamarxsen's Channel
The key is making YOU be exciting. Make it so your dog wants to come to you, and has fun while doing it. There's also a few things you can do in emergency situations like get on the ground, so that your dog looks at you and is curious as to what you are doing and comes over to explore. I saw this on It's Me or the Dog.
Basically, it takes practice. Jackson is a really well trained dog and I honestly think he'd probably be fine off leash but I still don't really purposely risk it. He does his agility classes all off leash and sticks by me for the entire hour class, so it gives me confidence. I take him to a big open beach with my aunt where her dog goes off leash but I keep him on the 50ft line still... I think he'd probably be okay but I'M too nervous. I think I just want to be 100 percent confident. I'm at about 99 percent right now.