To fix a dog that ignores the recall, you need to teach your dog that coming back to you is always a good thing, and will result in tasty snacks, a fuss, or whatever reward they like best. When you let your dog off their lead, a whole world of choice opens up to them. Your dog could decide that chasing a squirrel or playing with another dog is more exciting than coming back to you.
Teach your dog to respond to their name before adding recall, teaching your pooch their name makes it easy for you to grab their attention when you need it. Always reward your dog when they come back, start indoors, in your garden, or in another enclosed space with some tasty treats to hand. Add in some distractions and increase the length of the recall distance, gradually increase the distance between you and your dog and the level of distractions you call them away from. If your pooch keeps darting off when you call them, stick with training on a long lead attached to a harness, and only let them off-lead in secure areas. If you aren’t seeing an improvement with your dog’s training, you may wish to contact a qualified trainer or behaviourist to help. If you find your dogs recall isn't quite where is should be, it might be worth enrolling in some dog training lessons.