Stripping brackets from urls?

Hi

How can I stop brackets being stripped from urls that are being put in a custom field. I have affiliation urls that are using brackets inside the url just like this:

https://clkuk.tradedoubler.com/click?p(546785)a(1341234134)g(35463563)

When I click on the link being created by the meta tag the brackets are missing and as a result the url is faulty.