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I completely agree with Patrick. I can't reiterate enough, before you start blocking traffic make sure you do your research. For example semalt, a well known "spider" seems to send fake visits. Before you actually block anything, it might be worth just filtering analytics to get a true analytics of traffic. I try and view blocking/disavow as a last ditch effort. They will have the most drastic impact. Patrick included some great links, I highly suggest checking them out.

You do not need to use any special code like that, all you need to do is make sure that the basic Google Analytics code is located on all pages on your site.  The one thing I do recommend doing is updating to use Google's newest tracking code, which should look like this:

Have you tried Sprout Social?