Only Allow Something to be Posted Once

[Wally]

Is there a way to only allow an xthread field to be posted once?

For example, the video gallery. Is there a way to only allow a youtube video link to be posted once, and be disallowed from being posted again?

[ZiNgA BuRgA]

No such feature exists in XThreads unfortunately.
If you don't mind users getting ugly errors though, you could always stick a unique index on the URL column in the threadfields_data table.