Quote Originally Posted by Beleriphon View Post
Or just borrow heavily from Planescape's cant. Given that it was based largely on rhyming slang its a really good place to look first. As a plus it is already English, you just need to have weird work associations and a rhyming dictionary. Or as always The Google abides: http://www.cockneyrhymingslang.co.uk/
Or you could use Thieves' Cant, maybe?
That's a link to the full text of a dictionary of criminal slang, from the early 19th century, originally published in the very late 18th - 1785, I think.