I have 3 mango trees in my garden and my house is surrounded by a 4.5 feet compound wall. Random kids from my street tend to climb upon my wall and start to steal mangoes. sometimes they throw stones to get them, which falls & spoils flower pots in my garden. How to protect my mangoes and prevent them from stealing?
Prune the tree
Immediately after harvest this year, prune the tree away from the wall. Make sure that all the branches are well inside the wall, and lower to the ground. By making the tree less visible, and requiring people to completely climb over the fence you'll discourage most random casual theft.
Further, the tree should fruit more productively over time if it is well-pruned, and should you lose additional fruit to theft, it won't impact you as significantly.
Plant another tree
Another tactic is to plant another mango tree, thus producing twice as much fruit as you have now, allowing you to freely give the fruit away without worrying too much about whether permission was obtained.
Extend the fence up
Adding another 2-3 feet of lattice, wire, or bamboo fencing on top of your existing wall may be permissible (check your local building codes). Lightweight and inexpensive, it should be easy to install. Because it's not heavy duty, climbing over it would be an act of destruction, and will discourage many people from attempting.
The extension will also limit visibility, and make rock-throwing less successful.
Pinch buds at beginning of season
With a few minutes work a day at the beginning of the season, you can remove the flowers or fruit buds from the side of the tree that overhangs past the fence, and locations that are easy to get to from the fence. Just remove the buds or flowers by pinching and twisting.
The remaining fruiting locations will typically do even better than usual, as the tree will expend most of its energy on the surviving buds.
Maybe you can house your dogs closer to the MANGO tree. A tall fence sounds like it should work but will cost quite a bit of money. I would write a sincere notice, perhaps something like this:
Please do not steal my MANGO fruit. You are tresspassing and stealing fruit from my yard is a punishable offense. I have notified the police of tresspassers and they will be looking out for any offenders.