terriers are like (human) boxers they need built up gradually you wouldnt jump in a ring with tyson now would you? start them of slowly e.g a mouse, then a rat, then a squirrel keep them winning build up there confidence before you enter on there bigger apponents let them see the end of a dig so it all gets taken in and like said work on recall and stock breaking hope this helps im no expert as im still learning all the time