First idea is more simple: tie him up, go as far away as he is comfortable with, sit down (or stand) and just hang out there for a while. Give him treats, talk to him, and just genr=erally make it a good experience. Over a few days, slowly increase the distance, never going beyond what he's comfortable for.
More complicated, but perhaps more comprehensive:
1. tie him up, and give a treat/ praise him. (to show him that being tied up is okay)
2. start to move away
3. Once he starts barking (if you can catch it just before he starts to bark, that's good too, just skip to step 4), stop moving, wait patiently for it to stop, paying no attention to him (even if you haven't even turned around or started to move away, or if you have only taken one step away)
4. The second he stops barking, even for a moment, run back to him, (if you already moved away a bit) praise him, treat him, or play with him (or some combo of the 3)
5. Repeat this 3-5 more times. For one or two of the repetitions, untie him for a bit as part of his reward (showing him he's not stuck there)
6. Sometimes, mix it up by tying him up, starting to walk away, (either just act like you're going to turn around and go, or start walking away, or go briefly out of sight, whatever he's comfortable with at this stage) and then, before he has a chance to bark, run back to him and make a big deal over him.
7. Over the course of days or weeks, you should start to be able to go farther and farther away.
8. When he's getting a hang of this and will let you go 20-25 feet away, start walking away for 15-20 feet, then just stand there for a while before going back to him- this helps add duration. Start with just 5-10 seconds, and add time gradually.
More complicated, but perhaps more comprehensive:
1. tie him up, and give a treat/ praise him. (to show him that being tied up is okay)
2. start to move away
3. Once he starts barking (if you can catch it just before he starts to bark, that's good too, just skip to step 4), stop moving, wait patiently for it to stop, paying no attention to him (even if you haven't even turned around or started to move away, or if you have only taken one step away)
4. The second he stops barking, even for a moment, run back to him, (if you already moved away a bit) praise him, treat him, or play with him (or some combo of the 3)
5. Repeat this 3-5 more times. For one or two of the repetitions, untie him for a bit as part of his reward (showing him he's not stuck there)
6. Sometimes, mix it up by tying him up, starting to walk away, (either just act like you're going to turn around and go, or start walking away, or go briefly out of sight, whatever he's comfortable with at this stage) and then, before he has a chance to bark, run back to him and make a big deal over him.
7. Over the course of days or weeks, you should start to be able to go farther and farther away.
8. When he's getting a hang of this and will let you go 20-25 feet away, start walking away for 15-20 feet, then just stand there for a while before going back to him- this helps add duration. Start with just 5-10 seconds, and add time gradually.
