When I first got my keets, a friend also dropped off an adult male. The keets weren't ready for the outdoor coop / run area, so Henry had the rule of the roost. I kept him in that area for a month. During that time, I trained him to associate food with ringing a bell and was able to lure him back to the coop using the bell, followed by his food. I did have issues with him taking off and heading for the hills, but only when he was alone. After the keets got old enough to be in the coop area, he was put out to free range and wouldn't go anywhere! He just kept pacing back and forth in close proximity to the rest of the flock. I did have to eventually get rid of him because he never assimilated with them - he was overly aggressive and kept breaking up the flock and trying to pull off the females in his own harem.
I have never had a problem with the flock I raised from keets wanting to head for the hills, but I worked with them a lot to train them and get them to connect their coop with food and roosting. Again using the bell, getting them in at least 30 minutes before the sunsets, and making sure they have treats when they enter. I have since added 4 guineas - about a month younger than the flock - they get along okay, but really move more like a subgroup within the flock, but I had seen that even before the 4 new ones were added. There's the flock and they move together as one cohesive group, and then there are 2-3 sub grouping within the flock. The 4 new ones have never headed for the hills, they stay with the established flock.
So picking up on what Rhea said - I agree - they need a good month being held in the area where they will be living. They also may need some experience going in and out of the building. Perceptually, it's a different building looking out from the inside versus looking in from the outside. Some of mine had an issue navigating around the fence and getting in the door. Once they saw the other guineas, they thought they could go through the fence - super guineas!
On to your question about confinement. My flock of 12 range on about 10 acres. They are VERY happy - I can tell by their chirps and relative "quietness" compared to what I've heard from others. They LOVE making tunnels in the tall grass we have on most of the property and make themselves at home in the yards of our three neighbors - who enjoy having them there - we are lucky!
Could you keep them in a largish garden area with netting? Probably... I don't know how much it would stress them. It would depend on the how large the area was. Rather than netting the top, you could clip their wings. I would only recommend doing that if you are not going to free range them and you don't have to worry about predators in the garden area. Pattyhen on this thread has her two guineas wings clipped and they do very well in a fenced in yard with her chickens and ducks - in the middle of the city! So confinement isn't a bad thing - it would just depend on the space you can give them, how many guineas you have and if it works for you. So much of what we do with our guineas is dependent on what we observe and the adjustments we make based on our observations.
Hopefully, others will post their ideas as well. One thing you'll find on this thread, we're all willing to share ideas and we know there isn't any ONE right way to do things. Much of what we do is dependent on the kind of "farms" we have, but we sure do love our guineas and appreciate the support and ideas of others. Good luck and keep us posted on your progress....