Found this 21 for freezing the layers.
Is this code okay?
#model
ssd_net = build_ssd('train', 300, num_classes)
net = ssd_net

#freezing the first two layers
for layer,param in enumerate(net.parameters()):
	if layer == 1 or layer == 2:
		param.requires_grad = False
	else
		param.requires_grad = True

Is this correct anyone?