My brother and I have a wireless link between our houses with a line of site problem. We used a high gain directional antennae (dish type) to shoot through a few hundred feet of trees and then about a half mile to a old windmill tower the does a 90 degree turn and repeat to get the signals the other 100 yards to his house.
Using the high gain dish antennae and off the shelf wireless routers, four routers set up with four dish antennae can easily cover 10 plus miles of open land.
Starting with a simple router and dish as the first end, then five mile gap, another dish and router to router link then another dish, (for the repeater station) then the second five mile gap followed by a the last dish and router to connect the end point to.
I have heard that this can be done with a number of router to router repeaters to get around land obstacles and can cover vast distances while still providing a good reliable link.
Each repeater station router pair only needs about 5 watts of peak power input from a 12 volt source. That makes a deep cycle battery and solar power source viable if the repeaters dont have access to a local land power source.
100% legal, off the shelf, and rather cheap too!
Standard issue satellite TV dishes with a properly made antennae board can cover that distance easily as well.
with some scrounging and on line buying a 10 mile capable single repeater system can be built for under $100. Mine was!
For system security the routers can be coded to only talk to each other as well!