So that you don't always hear the annoying sound of the portal when you get near it, there's a remedy with this gadget.
The system is relatively simple. At the bottom block of the portal are two launchers. The left one contains a water bucket, the right one several fireballs.
By pressing the right button, the right launcher gets a redstone signal and shoots the fireball that ignites the nether portal. Now you can go into the Nether, do what you want there and then come back.
Now the left dispenser is triggered by the left button and it puts water through the water bucket in front of it and destroys the portal. By pressing the button again it takes the water again and the bucket is filled with water again.
And already you have an on and off switchable nether portal which only makes the noise when you want it. So it is also possible to build a hidden nether portal in multiplayer.