PHP REMOTE_ADDR security

Hello All,
My 1st post here! I have a contact form that submits all the info just great.
However, I get the occasional poster that just spams the form with tons of
links. I do have this disclaimer on the page itself:

The comments posted on the form are NOT in anyway posted
online on this, or any other website. I’ve been getting allot of spammers
filling out this form, and including hundreds of lines of code, all for backlinks
to their spammy sites. You will in no way inherent ANY IBL, or PageRank!
That doesn’t stop them. I want to exclude/deny their IP addys from the site
but the means of capturing the users IP:

$ipi = getenv("REMOTE_ADDR");

is not full-proof. I get users submitting with IPs such as: 127.0.0.1 - obviously spoofed/hacked.

So, what can I do to prevent the spoofing of IPs submitted vis that
REMOTE_ADDR function?