When we first adopted Mingus, we lived on a 1/2 acre property in a very urban neighbrhood in Portland, Oregon. We had purchased the place two years earlier, so I knew that on the 4th as well as the weeks before and after, the block became a war zone. I was worried how Mingus would react, but I had no way of closing him in his run-in.
Keith and I set up chairs outside his corral so we could keep an eye on him and waited for the first explosion. Our next door neighbor was the chief culprit, setting off huge mortars (illegal i Oregon) despite the tall firs on his and our properties.
The first launch was a doozie that exploded directly over our heads, shaking the ground and rattling our chairs. We winced, but Mingus stood in the middle of his corral, enjoying the show. His thought bubble read, "Wow...cool, due!" He spent that entire evening (and every 4th that we lived there) looking up at the sky. When Thelonius joined us, I'm not sure he was quite as thrilled, but he simply stood behind Mingus, watching from under his neck.
Now that we live out in the country, our horses hear gunfire frequently and think nothing of it. I worry more about our dogs, as I previously had one (Hillary) who was utterly terrified of the mildest of fireworks.