A slip lead is a safety lead used to prevent escape. It's used frequently by fosterers and adopters of very nervous dogs, and particularly foreign dogs, who are major flight risks - if they escape, you're just not getting them back. It's supposed to be temporary, until the dog has properly settled and is no longer a flight risk - some dogs always remain nervous, so always need it for their own safety.
It is NOT a replacement for training and it is NOT a training aid and should never be used as such.
Your DH is being cruel, and none of you should be using this as the main lead to walk the dog - it is used as backup, along with a harness and lead, which should be what you actually use to walk the dog.
I'll repeat - the lead is a safety measure. It is NOT to be used to strangle your dog (which is exactly a object that is designed to be escape proof and used round the neck will do).
If your dog is not a nervous dog, bin the fucking thing and use appropriate gear.
I've foreign rescue dogs that never lived in a house or walked on a lead until they were adult. You do not need to use a 'pop' on a lead to correct unwanted behaviour. Actual training does that.
And if you do have a nervous dog, you're not helping with your usage of this. Do fucking better, all of you.