Here is a quick tutorial for doing that in the social pro kit's facelook template.
Rename register.php to something like x3dqR758.php
It can be anything really. As long as it matches up with the code below.
Then open templates/facelook/header.tpl in any kind of text editor and find the line around 104
Code:
<a style=" color:#FFFFFF;font-weight:bold;" href='{$URL_register}'>{#PLIGG_Visual_Register#}</a> Change to the following, note you'll need to replace example.com with your own domain.
Code:
<a style=" color:#FFFFFF;font-weight:bold;" href='http://www.example.com/x3dqR758.php'>{#PLIGG_Visual_Register#}</a> That's all there is to it.
If you want go even further you do the following with the submission process.
Rename submit.php to something like 4Tr8jsvd.php
Then in the same header.tpl file find the following around line 155
Code:
<form Method="GET" Action="submit.php?url=">
Change it to
Code:
<form Method="GET" Action="4Tr8jsvd.php?url=">
I wouldn't suggest using my exact numbers/characters renaming posted here. The main idea is to make it something obscure.
Hope that helps.