.htaccess file is geting over written each time

Hi,

we have mutli site installed for sub folders and each time i edit .htaccess file it is getting over written again. i am placing new rules outside the #begin and #end . Please help

here is my htaccess file

# BEGIN WordPress

# END WordPress
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]

RewriteRule ^([_0-9a-zA-Z-]+/)?wp-admin$ $1wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-(content|admin|includes).*) $2 [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(.*\.php)$ $2 [L]
RewriteRule . index.php [L]