You can use this to show it members of certain usergroups. Simply edit the "in_array" below to add usergroups to it.
This will add a "reply" button next to the newthread button.
Even if a bot is aware of the newthread & new post buttons, they will no longer follow it with the nofollow attribute, additionally they won't see it if you configure which groups can see these buttons correctly.
Go to: ACP --> Template --> thread_view and find:
<xf:breadcrumb source="$forum.getBreadcrumbs()" />...