In order to clarify the process I think I'll post a riddle that someone submitted earlier today. It needed some modification to work properly in this context, so I'll use it to demonstrate the general idea and the sensible boundaries of the contest. We'll consider it a trial run.
* SAMPLE RIDDLE *
Transient, noticed by few,
Above the answers I perch.
Travel there by sentinel,
To find me you must search.
Longer than you might think,
Free me with a name.
Hobbitsis knows the password,
Signposted by a game:
This key all things devours:
Birds, beasts, trees, flowers;
Gnaws iron, bites steel;
Grinds hard stones to meal;
Slays king, ruins town,
And beats high mountain down.
* SAMPLE RIDDLE *
Text in blue was added/edited by me in order to make the riddle work within the bounds of this contest. The point here being that the riddle must be specific to the forum. Taking an existing riddle and extending it is fine, but original is better.
If you can solve the riddle great; if not I'll explain it showing the sort of information needed in a submission. I'll also explain why the answer is possibly not the best sort of URL to select and why the original author's URL is inadmissible (I picked a similar one to demonstrate the point).