Don't put in a pool. ;)
As the other poster said, especially if this is the first full season with your fully-equipped (awesome!) deck, I think you'll need to set up some boundaries. Maybe first by just acknowledging your friends -- chatting through the fence a bit and then saying, "It was nice talking to you but I need to get back to the grill/my husband/the show" or similar. Occasionally you could throw in, "We should get together next Friday. Want to bring something for a cookout?" The first response acknowledges them and lets them know gracefully that you're not going to be inviting them over right then. The second recognizes that you've got the best deck ever and that they're preferred guests --just not all of the time -- and you want to plan those times. (The drawback to this is you might have to start planning all summery evenings you get together a little in advance so they don't keep thinking, "Maybe this time we can come over!")
If those don't seem to stick, maybe say, "How about we set up some regular times to get together? We love having you over, but sometimes we're not great company. We just want to relax and unwind."
Not sure if your kids are still around, but if so, you might have to let them in on this because they might invite your friends' kids over not knowing what you're trying to put in place.
Most of all, make sure you and DH are on the same page. With the occasional invites to come over, I think your neighbors will settle down. I suppose you could look at it as a good thing that they don't just pop over unannounced! :)
Good luck - please let us know how it goes!