Outdoor lighting: use 12V transformer or 220 V mains? And use RCD or not?
Your design is dangerous because you don't have safe light fixtures. Outdoor light fixtures, especially at 220V, need to safely insulate all electrical conductors. In an environment full of moisture and active, moving animals, you need fixtures that are secure and sealed. If you can't buy these, maybe you can make some, but don't expect regular indoor fixtures to be safe.

Let's think about how this system gets dangerous. Some of the wiring gets exposed, and a person or animal gets between the hot and neutral legs, completing the circuit. This could happen with two adjacent puddles of water, maybe one touching a hot and the other a neutral. Or a puddle and a rake that's pierced some of your above-ground cabling.

Your "ground" wire doesn't help. Bonding neutral to ground is good because it means that a loose hot wire that touches some exposed metal (or other good conductor bonded to ground) will blow the fuse quickly. You're not in an environment with lots of good conductors; even wet dirt may not conduct well enough to blow the fuse. If you had for example a metal walkway and a nearby metal pipe, you should definitely bond those so they can't be separately energized. But if you're just talking about an electrical system out in a field, bonding the field to neutral doesn't buy you much.

An RCD (residual current device) or GFI (ground fault interruptor) may not help much either, because again you're not likely to leak current to ground. However, these might be a little more sensitive than your fuse so they could help a bit.

The safe approach here is to use proper light fixtures designed for outdoor use in wet areas. These can be low-voltage or high. Low voltage is safer, because even if the fixtures or wiring fails the available energy is not enough to kill you. But a 220V setup that includes sufficient protection for your junctions and the light bulbs would also be relatively safe.

If you stick with your design, at least realize that your ground does not make it any safer. Protect your fixtures and junctions from moisture and from access by people and livestock.