vincebodie
Hi
I will share the suggestion to concern team, its not a simple implementation, it needs planning to check the possible ways.
The Joomla ACL only work for group.
To hide he frontpage activity for public, open Configuration > layout > http://prntscr.com/kyrpf0
Set it to Members only.
To show the activity only for friends change it to me and friends : http://prntscr.com/kyrpg9
For ACL you site does not have guest user group that is used in Joomla by default. It seems its deleted and ACL is customized, i am not able to replicate this issue in fresh package, can you check it on demo site here
Regards