I have been doing some reading on the topic of cross pollination distance recently myself as I am dealing with a 5 acre property with many mature trees, and now trying to find places here and there to insert more fruit trees. Unfortunately finding good information is not that easy, and you generally run across a rule of thumb that says plant 2 trees that will cross pollinate if within 75 to 100 feet of each other, and maintain at least 500 feet to 2 miles of separation to exclude cross pollination in fruit trees. A bit more digging and one finds that not all fruit trees are the same when it comes to pollination, and that pear tree blooms are not nearly as attractive to bees as stone fruit blooms are. Now when one reads about honey bees, one will find that they will range up to 2 miles from their hives searching for food, and that they tend to back and forth along the same basic angle. Of course there are other types of pollinating insects other than honey bees, (other bees, wasps, moths, etc.) bumble bees are another common pollinator though they are less reliable than honey bees and lack the ability to coordinate foraging so tend to roam around at random over much shorter distances from their hives.

Having said that, you mention that you are dealing with the back yard of a 1 acre lot, 1 acre square is about 208 feet on each side, assuming a typical rectangular yard that is 3 to 4 times deeper than it is wide with the house set 1/3 of the way back from the front edge. So for easy math lets assume a backyard that takes up 2/3 of the total lot (.66 acres), that is a bit longer and narrower than average with the total lot measuring 100 ft x 450 ft (1.03 acres), and the back yard portion measuring 100x300 ft. It is easy to see that at no point in the back yard can 2 trees exceed the minimum 500 ft separation suggestion to prevent cross pollination and also it is fairly easy to stay within the 100 ft cross pollination distance guidelines one commonly sees in print. So in the end you probably should not worry too much about it, just don't place plants that you wish to cross pollinate at opposite corners of the yard.

Yes...lots of people worry too much about cross pollination, no need to graft into the tree, it can help by planting them in a good mix, I'd still plant the harder to pollinate fruits together, like plums. That permaculture thing..a bit of a hype I think lately but it can be good, definitely not a miracle thing..you'll still get pest problems..perhaps less airborn/spreading problems, say if you're in a environment where it's wet allot you have fungal/virus problems no matter where the trees are planted, probably need to get sprayed if you're wanting to harvest anything, especially stone fruit.