Prevent Apache RewriteRule from repeating

Question

I'm creating a webDav client, and using an external php script to redirect users to their appropriate folder. I'm unsure about my rewrite rules - I want to make sure they only get fired off at most once each. From what I understand, this is the case, but each time I access the page, multiple access are made, so I'm guessing the rewrites are being called multiple times

RewriteEngine On
RewriteRule ^/webdav$        /webdav/
RewriteRule ^/webdav/(.*)$   WDM:%{LA-U:REMOTE_USER}:$1
RewriteMap     webdavmap     prg:/Library/WebServer/WebDAVHelper/redirect.php
RewriteRule ^WDM:(.*)$   ${webdavmap:$1}

<Directory "/Library/WebServer/WebDAV">
    Dav On

    Order Allow,Deny
    Allow from all

    AuthType Basic
    AuthName WebDAV-Realm

    AuthUserFile "/usr/webdav.passwd"
    require valid-user

    Options +Indexes
</Directory>