We got rid of our trampoline as i didn't feel it was being used safely
I love the idea of sinking it which would have been great but not an option for us.
Dcs were the first round here to have a trampoline,(brought it with us from our old house) Therefore we had endless kids queing up to come in and have a shot.
It caused nothing but fights and arguments about who's turn it was. One thinking that someone else had a longer turn, The "he/she, pushed/jumped on/kicked me" whinging.
Not undrstanding that 10 kids cannot go on at the same time!
Not to mention some kids deciding to go under the trampoline when the others were on top, Then complaining because someone jumped on thier head.
Ours had a safety net but over time was torn and stretched, The poles were bent beyond belief with the kids pulling and leaning on the net.
Somehow someone always managed to get pushed off through one of the holes.
I called it a day when i caught DD who was about 5 at the time trying to jump out of my DS bedroom window down onto the trampoline (was directly below) which i then found out that she had seen her older brothers doing previously!) 
I was costantly worried that someone would damage their back or neck when they were trying to do flips that they'd seen on the tv
Also with 3 dc's and all thier friends i couldn't supervise every time it was in use as i would have been out there for bloody hours....In the end i got sick of my own voice trying to sort out squabbles and telling them to be careful so it had to go. It was the best thing i did.
If a trampoline is being used responsibly then it's not always necessary for the net.
(As in my case kids still got pushed off through the holes anyway)
But obviously is safer with one. I would never again have a trampoline.