Possible Clues:

• Spiky (of bush or problem)
• Troublesome old god somewhere in the US
• Spiny — difficult and controversial
• Prickly, problematic
• Troublesome or difficult, like briars?
• (Of problem) causing difficulty; prickly
• Nettlesome
• Cut off the top of what's prickly and it's still sharp
• Nor in your prickliness
• Instrument in time variable and problematic