IF you want to change your major, How about a VET?

I did a google search and came up with lots of web sites.
Here is one:
http://www.pk9.com/documents/policy.html

If you want to be a police officer.
I would think you would need to contact the different
law enforcement agencies in your area.
They should point you in the right direction on whom
to contact for k-9 unit information. Not every area
has their own k-9 unit and each county/or state might have their own requirements.