Nylabone
Hooch is showing the regular flavored nylabone, although he prefers the chicken flavored nylabones.  These last much longer than any other chew toy and are much safer because they do not cause bloat.  And so long as the nylabone is taken away after the knuckles are chewed down, there is less of a risk of choking.
 

Kong Toys
Casey tested and approved!  Fill this up with peanut butter and your Bullmastiff will be busy for hours!  Great as a separation anxiety deterrent!