How to tell when user click link to other sites ?

I have a simple hyperlink on aspx page that link to outside website.
<a href="http://web.com/" >Somesites </a>
I wish when the user click on the link, I add to database the time, the user name and most important which link s/he has clicked everytime s/he click the link because I want to make sure users have read some important document.
I have the time in label1.text and username in label2.text on the page already.
How to get the site name he clicked to label3.text ?
Is it I need to use ASP.Net supplied hyperlink control instead ?