I like the approach that suggests the best hiding spot is in plain sight. Namely, what about choosing your planting sites beforehand, and figuring out a way to prep the site so that it looks like a municipal
project? I can see this working better with seedlings of any size, where you could run up with a potted seedling, rip up a circle of sod, drop it in, plant it,
water it, and perhaps mulch heavily with something that looks close
enough to beauty bark, something like ramial
wood chips or chipped bark. While I don't like interfering more than necessary, I'd add to this a trunk cage (to be removed soonest) and maybe a flag or any type of support structure common on authorized municipal plantings. The most effective guerillas are those that look like they're supposed to be there. I even like the idea of cheaper commemorative plaques mounted on small rocks or something (especially if you can arrange rocks decoratively for the purpose of the plaque and have them also regulate temperature and sieve moisture from the air) that resemble those purchased for donors of
trees or park benches or the like. You could do up a fake commemoration, or you could be completely blunt about the unauthorized nature of the tree.
Having said that, you could take all these steps and use seed balls, but that would increase your time in the spot over just chucking a seed disc.
-CK
A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects.
-Robert A. Heinlein