How to train a dog to use the toilet in the same place

My dog is ruining my grass.

I wondered if it would be possible to train a dog to use the same place when going to the toilet?

We have a patch of grass at the bottom of the garden which is probably not going to survive and thought perhaps we could dig it out and place bark or something down there as a toilet area?

Any tips?

I've seen things called pee posts which have a smell on them which is supposed to encourage a dog to wee in their vicinity. No idea if they work or not though.
Will your dog wee on the lead? If yes take it down to where you want the business doing and wait for the magic to happen, when the dog has done its business treat and praise.
Repeat repeat repeat and hopefully more wees should happen where you want them too and less on the lawn (hopefully being the operative word )

On lead and take to the area every time.

If you can section that area off so that it is more of a 'definite' area so much the better.

Plenty of reward for going there of course - play, treats, praise - keep the rewards varied.

Of course you could always put the lead on and take it OUT of the house whenever you think it is 'time for a pee'. I have to do this anyway because I live on the 4th floor!

If the dog has the free run of the garden in and out all the time I don't know how you can stop it.

I mean my dog will go all day without peeing sometimes but once she is outside she pees on every corner, every scrap of waste paper, everywhere else another dog has peed!

As others have said plus you need to give the cue as the dog is circling or doing whatever it does beforehand. The cue needs to be given just before, so the dog makes the association. Much easier to do with a pup but with patience, it can be trained. Watch your dog on walks and just before moment, give the cue, such as "Pee time" to put the cue under stimulus control.