At first, the obsession with conventional degrees will be a hard nut to crack.

FORBES: Free Education Is A Meme Whose Time Has Come

England scented a rout, but found the sixth-wicket combination of Mashud and Mushfiqur a hard nut to crack.

BBC: SPORT | Cricket | Ban v Eng 2003 | England take control

Many companies have tried and failed to break the US market, but it has proved a hard nut to crack for UK retailers.

BBC: US Tesco brand Fresh & Easy 'wasn't aspirational'

Of course, breaking into schools is a hard nut to crack.

FORBES: Tech Startup CodeHS Aims to Bring Computer Literacy to High Schools

This is a hard nut to crack.

WHITEHOUSE: Press Briefing