If you want your dog to have better attentiveness, work on the walk first. Get a prong collar and teach your dog how to walk without pulling, marking, sniffing...
A dog cannot be in “follow” mode and “hunting” mode at the same time. Get your dog’s nose off the ground so he stops “hunting”, teach him to walk by your side instead of way ahead of you dragging you with all his power so he starts following.
When you can get the dog into follow mode via implementing a more precise “heel” with the dog’s nose off the ground, no constant marking, no massive pulling..., you can then teach the dog how to sit and down. Prong collar tension upward means sit, pressure downward means down.
You can apply these two commands in your walk with your dog — when you stop, you pull up on the leash, your dog sits; when you sit down, you pull down on the leash and your dog goes into a down by your side. Make sure the dog holds the command until you start moving again.
Try to do all these without saying anything. Try to “talk” to the dog with collar tension (when tension is felt, the dog will think and try to ask himself which direction is the tension coming from and choose to yield to that direction) and your body movement (when you move, he moves at the same pace; when you stand and stop walking, he sits; when you sit, he downs).
If you can only teach your dog these three things, you should already see a significant improvement in your dog’s attentiveness.
It is because these three things nurture the dog’s follow mentality — he will want to follow you as his leader when he is in follow mode — a dog who follows is a dog who is attentive; a dog who is attentive is a dog who is less impulsive; a dog who is less impulsive is a dog who is much more capable in making better decisions.
Hope this helps.