(I will answer this question for the enclosure (unsupervised) only. For the daily garden movement you need the "rabbits stay in" rules and can read the question Should I be worried about neighbors' cats in the context to my outdoor rabbits? )
First you should know which rabbit-specific predators are common in your area. For Western Europe these are foxes and martens.
So your boundaries have to hold foxes, martens AND rabbits in place (the first two at the outside, the latter one at the inside).
[Edit: What to do, if you have raccoons in the neighborhood, you can read here: Racoons: What sort of protection do my rabbit enclosure need? ]
It should be point-welded. This means that every crossing of the two wires should be welded, instead of woven-wired. In case of woven wires it needs only one cut and as a result the majority of the grid could get ripped apart, so rabbits or predators can force themselves trough.
If you use thin wire (more than 1 mm / 0.04 inch), the grid spacing should not be larger than 19 x 19 mm (0.75 x 0.75 inch), so the rabbits can not use their teeth on it. Bigger grid spacing have to be from thick wire (which the rabbits can not bite in pieces).
Martens are the smaller predators. It can squeeze through gaps of 4 cm / 1.57 inch, so all grid spacing should be smaller. Martens can are strong and capable of bending the wires, so the bigger gaps should be reliably surrounded. (For example, some manufactured rabbit enclosures use grid of 3 x 5 cm rectangles. This could be bent by marten, enabling it to fit through the resulting 4 x 4 cm gap.)
There is a saying here: if a chick's egg could fit trough, the marten would be able to fit through, too. (In fairytales, martens are the chicks' killers).
The wire should be processed in the context of corrosion-proofing, for example galvanized, to withstand the weather (rain → rust).
The grid has to be properly attached. Attach it with full rectangles, not with only protruding wire-ends. Make a pull test.
Optional: insect mesh.
If you are worried that your rabbits could get infested by maggots or infected with myxomatosis, you can use these special curtains on the wire.
Requirement: prevent rabbits from digging their way out, prevent predators from digging their way in.
If the enclosure foots on solid flooring, it is useful to sink stone plates ore grid between 30 and 100 cm deep in the solid flooring (12 - 40 inch).
A other possibility is to lay a 30 cm wide stone path on the inside of the fence around the enclosure.
On both strategies, one has to estimate the digging effort of the rabbits, but because the potential digging distances are long, the rabbits cannot dig an escape route without being noticed.
More building effort regarding the next two suggestions:
One could remove the complete basic solid flooring of the enclosure, lay grid into the ground and fill the hole. Or one could lay stone plates on the ground flooring, all in the enclosure.
Martens are very good climbers, so it is useful to close the upside of the enclosure (especially if they are small) with grid too (see point grid). Web does not suit there, an exception is wire-web, but this is very expensive.
If the fence of the enclosure is larger than 2 m / 79 inch, one can add a second part above. This should be tilted about 30° to the outside. One could find such things for cat-security (designed to hold cats inside) but use it opposite (to hold martens outside). This 30° part should be very smooth (in other words, it shouldn't be possible for predators to get a foothold ) or with an electric fence (like the one for horses or cows).