Dig two holes in the ground on either side of your sidestay chainplates and put a plank or 2 by 2 in it. Tie lines to these and burry then. These are called ground anckors. Position your boat i the middle and tie it off to the chainplates or even using the trapeze wires. Fro grassland the same will work but here special spiral ground ankers can bought that screw themselfs in and are strong enough. We use these methodes all the time here on the beaches and we do get some major storms during our sailing sailing.

When expecting a hurricane than it is best to take of your mast as well as these storms are strong enough to uproute houses.

Wouter