Hide wp-admin for multisite running on NGINX server

Hi There,
I'd really like to rename wp-admin to something else...anything really!! Let's say /dashboard however I'm not sure the best way to go about this and wondered what current advice on this topic is.

I run a multisite with about 100 sub-domain sites - 90% of which have mapped domains (using WPMU dev domain mapping plugin), and everything is run from an NGINX server. I was wondering how you think would be best to achieve this.