The biggest mistake people make. If you call your dog and plop him into the bathtub, or worse, leash him and take him home from the park, why would he come next time? If you need to call your dog for something he won’t enjoy, just go get him – don’t ever use recall.
Work at your dog’s level. Right now he’s somewhere in pre-school. Calling him away from an exciting squirrel is more at the collegiate level – he’s not ready for it. If you call and he doesn’t come he just learns that the command doesn’t mean anything. Teach the command ‘on lead’.
A failed “come” must be saved. Maybe it’s a bit beyond his level, or there was a distraction. Save the recall by running to your dog – put a treat in front of his nose, and back up so that he come toward you. Not as good as the real thing, but very important to have him go through the motion rather than letting him ignore the command.
Repeating does not make it so. Saying a command over and over doesn’t make your dog understand better – it just teaches him to ignore the sound you’re making because it doesn’t appear to him to have any meaning or consequence.
Think meaty treats rather than dry biscuits. If you expect your dog to stop whatever interesting thing he is doing to come running to you, the person he sees every day, you have to make it worth his while. Use High Value treats.