I don't have ideas for them, but "a couple mile's worth of line" is not typical for kites. That is a lot of line.
Most nations have a maximum height limit before additional regulations kick in. In the US that's 400 feet. In the UK that's 60 meters, about 200 feet. Other nations all have similar restrictions. Anything over those heights requires clearance from the local aviation authority like the FAA or CAA/CAO or similar.
Being at "a couple miles" puts you in the flight path of non-commercial flights, and 5 miles gets you to where commercial jets fly. Low-flying flights like medical helicopters or areal surveys commonly have a 1000 foot / 300 meter flight height.
Because kites fly at an angle you can have a little more line than that, that's often around 500-600 feet of line before hitting the 400' flight ceiling.
Also, reaching those heights will have significant other issues, atmospheric winds are different than what you get near the ground. Extremely high winds are common, with air currents reaching what would be tornado speeds if they were on the ground. High altitude streams and jet streams can reach several hundred miles per hour.