Q: How high should the fence be to contain an adult ?

A: I would build the Aldabra fence higher than the Galop fence.
Also it depends on what the fence is made of. A blind fence (a fence they can't see through) for a galop; maybe 3 feet, but it depends on the animal's size. For Aldabras, make the fence higher. They are more mischievous than the Galops, 
plus they will pile in the corner and jump on each other to get over the fence. (See my Video) 

I have seen Aldabras jump a 40 inch fence when they were only 12 years old, but this goes back to if the fence is a blind fence or open (see-through) fence. When a fence is blind, (a block wall or a stockade fence) they can't see through it so they won't try and jump.  

But those little devils, if they can see through that fence, they will never stop trying to get past it.  In my videos you can see an open 2x6 fence around my pens. It’s not good for containment, but I like to be able to see the animals as I walk around or from my back deck. When I sit on my chair at night, I like to watch them carry on. 

If I had used a blind fence then I wouldn't be able to see them from a distance. I build my pens with a high back wall (6 feet stockade fence), then inside the fencing I use 4x4 post cement in the ground at 4'centers and 2x6 horizontal boards with a space in between the boards so I can see through. But as the Aldabras got older they started snapping the 2x6  boards,  so I went to 2x8. They held them as long as they are not really motivated,  because I have seen them snap 2x8  

In some places. I have 2x10" boards 8 feet across as an inside gate.  they were on it the other day and started to crack it before I could stop them. 
That's just an internal gate between two pens so I am less worried about that gate.

Unfortunately,  I gathered all this understanding of their behavior over time. But while I was learning, so were the Aldabras.  
They devised many ways over the years to break a fence down. Every time they came up with an innovation, and I had to find a way to make the fence and the gates stronger.

For me now the damage is done; they know if they work at it long enough, they will get through any fence.  I am sure they have that level of understanding.   
The animals are smarter than you think, I can tell you for sure, they are very subtle, quiet and calculating in their own way.  

After so many years I have learned to read them better.
How to interpret their subtle body language,  just the way they move their eyes, or tilt their head.  I know.  I can tell spring has turned into summer or fall into winter, or they want the greener grass on the other side of that fence.

To you its a fence, to them it's an obstacle.

Sam