Complex sentence: Its relatively exposed position, in a county so near to German occupied France, meant it was potentially vulnerable to a German airstrike or commando raid; as a precaution, the lakes were covered with brushwood to make the house less identifiable from the air.
Split into simpler sentences: Its relatively exposed position in a county so near to German occupied France, meant that it was vulnerable to a German airstrike or commando raid. As a precaution the lakes were covered with brushwood to make the house less identifiable from the air.