First, a well made fire pit contains the fire, especially if you have a screen. Most fire pits come with screens that will keep hot or burning embers from popping out and landing a couple of feet away on a flammable surface.
A DeckProtect under the fire pit will protect your deck from heat radiating from the fire bowl and from any burning embers that land on the DeckProtect, but it will not protect your deck from embers that fly out and land farther away. The screen is really important for this reason.
A lot of people like to roast marshmallows or hotdogs on skewers over the open flame. Some fire pits have a grill that sits over the fire and enables you to grill hamburgers or other food and get that real wood flavor. When you do this, you have to remove the screen. The solution is to simply keep an eye on the fire. Don’t leave it unattended. If you hear a crack or a pop that sounds like a ember may have flown out, check the deck around the area. Have a bottle of water handy so you can dowse a landed ember before it does any harm.
Whatever you do, don’t conclude the screen unnecessary and chuck it out. Keep it close. If you have to step away from the fire for even a minute, place the screen over the fire.
At the end of the evening, make sure the fire is completely out and the remaining charred wood is no longer hot. One way to do this is to pour about a quart of water on it. Surprisingly, the next day… if it hasn’t rained, the remaining charcoal will be dry. Then cover it with an appropriate fire pit cover to keep it from filling up with rain water.
An hour or so after you have stopped using the fire pit, make another check of the deck and area around the fire pit to make sure there are no smoldering embers. Sometimes embers can fall between the deck boards to land on potentially combustable material below.