Complex sentence: The cast was made and given to the garden by George Bullock in 1918 and has remained behind locked doors since around 1950 to prevent people from cutting off pieces of the statue to melt down.
Split into simpler sentences: The cast was made and given to the garden by George Bullock in 1918 and has remained behind locked doors since around 1950. It stays locked to prevent people from cutting off pieces of the statue to melt down.