The most efficient way is to white list yourself using the directive designed for that task.
Order Allow,Deny
Allow from 123.456.789.123
Where 123.456.789.123 is your static IP address.
When using the "Order Allow,Deny" directive the requests must match either Allow or Deny, if neither is met, the request is denied.
http://httpd.apache.org/docs/2.2/mod/mod_authz_host.html#order
Or you could do it with mod_rewrite like so.
RewriteEngine On
RewriteCond %{REMOTE_ADDR} !^123.456.789.123$
RewriteRule .* - [F]
Note that 'RewriteEngine On' will be redundant if you already have placed in your rules above this one. So if that's the case you can discard it here.
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