Uno with 2 transistors for the motors, 433 MHz one-direction RF receiver, and simple MP3 card for sound generation.
http://www.mdfly.com/index.php?main_page=advanced_search_result&search_in_description=1&zenid=a97e40d5329464b68612f7146209f183&keyword=mp3
Can play different bark sound every time.
How loud does dog bark need to be? Use some old self-amplified/powered PC speakers. I have a set of old Gateway2000 speakers connected to my laptop at work. I have a set of Dell speakers with subwoofer I use at home.