Counter to turtling

[Joggies]

There are two responses to turtling:

1) Attack heavily on their weakest side (either a bonus square or a base flank). This could force them to readjust their army giving you a decisive advantage.
2) Turtle better than them. Trade punches efficiently and eventually you'll earn an advantage great enough to press them.

The greater the skill differential the more likely strategy 1) will work. Against a good player you just have to hope that you're slight skill advantage means you can trade punches for long enough to slowly win by attrition. A turtling match between two proficient players is a combination of a fascinating and excrutiatingly boring match, all at the same time.