Limiting Who Has Single Mode Access

Say what?

You can't...but why would you need to limit their ability to do their job?

Purchase Enterprise.

Because it isn't there job to change sensitive global settings for the entire company.

In Enterprise, will that be just a normal security setting for each user to select whether they can enter Single user mode?

?? Are you letting them log in as the admin?! Otherwise it matters not single or multi, they can only change what their settings allow. If you gave them delete permission single user lets them delete list items, that is all. So they make a typo and enter a new vendor as AR&R not AT&T. They may need single user to fix the typo when they find it was already there under A T and T. And they might need the closed periods password to fix this too, if they used the one with the typo to "merge" them.

I suspect you gave someone permission to do sensitive actions and didn't realize all the actions you were giving them. Check/change their permissions.

Single vs multi-user mode is not your issue. Read the help file on user permissions. Each user should have their own login and password. Then select what areas and what functions the individual can perform.

Enterprise gives more options but is overkill for most companies. You should be able to setup proper permissions using Pro/premier.