Security surrounding URL input

Hi,
  I have a website which allows users to enter URLs into the database. Other users can then view the person's profile and click on the URL. What security precautions should I take into account? I've heard I should use URLEncode, but I'm not sure when to use it. When I display the information to the user, I don't want to them to simply see "%2" instead of a "/". Are there any other security measures I should take?

Thanks


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