where can I add custom validation to the website(url) profile field (using profile manager)

I am using the profile manager and imported the default profile fields, but the website field's validation is not perfect. You have to enter http protocol to pass the validation. mysite.com and www.mysite.com won't pass the validation. Funny thing is if you enter http:www.mysite.com, the validation passes and insert a http protocol before it like http://http:www.mysite.com, which is totally wrong. I tried to look into those files but could not find where I can add some custom validation, can anyone give me a hint? Thanks