This is a little dog. He is under eight pounds. I will not be taking him outside on a leash until he can tolerate it without going berserk. He is currently at a rescue and much about his former life is simply unknown. I have a harness that fits like a vest. I will have that put on him when I go to pick him up. I have a soft sided carrier to transport him. Apparently, he is crate trained. He will use a piddle pad, so I don't need to take him outside to do his business until he is trained. My plan of attack is to show him the leash and have him sniff it and then maybe snap it on the harness and let him drag it around the house for a while every day and then go from there. I do know he likes treats. Anything else?
I would start even smaller then that even! First step would be to show him the leash reward and reward him, keep the leash at a distance from him where he is aware of it but not showing any major signs of stress. If at any point in training he does show any major signs stop the session and next time go back to an easier step
Keep the sessions short 2minutes about or less but do multiple a day, food rewards will be the easiest. Its best to have something small and fast for them to eat, most of the time people use something high value but you can "force" some dogs into something they aren't comfortable enough in doing with food so you do need to watch him closely
Break down the steps a small as possible and remember to go at his speed!
1. If he is extremely scared of leashes you can start with simple picking it up and scattering food on the floor at a comfortable distance for him, if you do this randomly throughout the day he will learn that you picking up the leash is a cue for good things. If he doesn't react to you picking up the leash thats good!
2. You can work on rewarding him for any interest in the leash you are holding. Sit somewhere and if he even looks at the leash mark and reward, some dogs love having the treat thrown for them so it might help to throw the treat away from you every time or you can do it every few treats to give him a small break
3. Next you can work on dragging the leash on the floor at a distance away from him where he is comfortable. Start with a very small movement and reward frequently. Don't move it towards him
4. You will probably need to work on the clip noise as well! Same as most of it, keep it at a safe distance make the noise as quietly as you can at first and reward him for every time
5. Then work on it coming towards him you might want some way he can opt in or out. Having a choice helps animals a lot with this type of thing! What you will want to do is have something either like a chin rest or just standing on a mat could work, you want to heavily reward that position and build a good reward history. Once you have done that (it will take a few days) to use it, its very simple If he is in whatever position you choose you move the leash towards him. Go slowly and reward frequently for it coming closer, if he moves out of the position then stop what you are doing and let him decide if he wants to come back
6. Once you can get the leash on him start with very short heavily rewarded sessions with it on him. And slowly build it up