So,
- web site have a user profile
- user can edit own profile
- profile data have "site" data field
- user can enter some site url and after that this url will shown in profile like a link
if user enter site with protocol (https://facebook.com ) there is no problem and it goes to https://facebook.com
but if user enter something like this facebook.com it will be internal link and goes to https://my.site.com/facebook.com
how can i avoid this situation?