Winter crop protection- hoops

Hello

I purchased large aluminium hoops with the hope of using them with horticultural fleece to protect my crops during winter. Ther are 1.52m wide 800mm high (Approx. 5ft x 2ft 7ins). Unfortunately they keep falling over. I have just started planting my allotment, and there is a layer of silt/clay at a dept of 15/25 cm. The plants don't mind (the compost helps) but securing the hoops in the ground is difficult. The plot is very windy which doesn't help either!

Any suggestion would be appreciated :-)

Many thanks

Vanessa