I've tried several "geo blockers" and while all of them work, most of them are very easy to bypass. The "Unicorn Geo-Blocker" has done a very good job of blocking countries.

It's a very simple APP to install. After installation just "type the message" you would like users in "blocked" countries to see, select the countries you want to "block" and then click the button to "enable"... That simple.

PROS:
Very simple to install and set up.
Ability to customize the "message" blocked countries will see.
Easy to "enable" or "disable" with the click of a button.
APP doesn't slow down your page or "wait for verification" before displaying your page to your customers in "unblocked" countries.
Excellent support from developer.

CONS:
None

FINAL NOTE:
After I installed the geo-blocker, the only thing I didn't like was the phrase "BLOCKED" "this store is not available in your country. I wanted something a little softer sounding like "Sorry... this store is not available in your country", or "Sorry, we do not have shipping options to your country".
I asked the developer if they could change the text for me...and within a day the option to add custom text was added! 5 stars for APP performance and excellent support from Darryn.