Hi Don Ferris,
You can secure a MODX installation easily with this two step!
1. Make sure your MODX is up to date. Like this, there no security breach!
2. Change the manager folder name. Like this no robot will find your manager login form!
Forget your experience with WordPress! Without doing this two step, none of my MODX installation have been hacked. Wordpress is the first CMS that hackers try to hack, because a lot of websites are made with WordPress.
I hope this help.