How do I stop wasps making nests in my sofa?

The sun has been shining now for a week, and already I have caught one wasp trying to make a nest in between my cushions on my sofa which is outside on a covered terrace.

This started to happen last year, but this year my four year old loves to play on the terrace and I am worried he is going to sit on a nest.  Any ideas as to what I can use to deter them?

Sam

Well, I saw a little piece of advice on the BBC pages which advises simply blowing up a paper bag (it says one as big as your head), tying it off and hanging it round the area you don't want the wasps to come.  Apparently, they see this as a rival nest and avoid it.  I wasn't too sure about this but then saw this little snippet from the eliminatewasps.org website:

One wasp deterrent, which can be purchased or made is a faux nest made of paper.  In this case, you would hang the fake nest away from the area outdoors where you hang out.  Typically, wasps like to build nests in areas that are quiet so hanging a faux house under an eave on the far side of the home would be a great option.  Colors and even patterns associated with a “decoy nest” add to the effectiveness.  

So it seems they agree.  Worth trying, I suppose.