Forms - disallow submissions with links in the comments (textarea) section

I created a contact us page that has a plain text textarea for comments.
Is there a way to not allow users to submit a form that has a link in a textarea? I am using the block form inside concrete5 which creates an express form.

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Gondwana replied on at Permalink Reply
Have a browse through this:

It isn't watertight (especially with all the newish weird TLDs).