The majority of Sirus' excersize comes from tearing around the house and the yard, and at my parents house and and in their yard. During the Summer in Vegas...which it is now...Sirus doesn't get to go on walks...even in the evening...because the temp. likes to stay right around 95-98 even after the sun goes down, so our walks would last 5 min.
In the fall, winter, and spring though...Sirus loves his walks.