Protection devices for a power MOSFET 1500V

Dear Sir,

An n-channel power MOSFET 1500V is used as voltage regulator 1000Vdc.
The input is 1200Vdc,unregulated,and the output is 1000Vdc,regulated,
and with current flow 250mA,in a capacitive load.
For the protection of the Gate to Source path I used a 12V zener.
In the output,between Drain and Source,internal protection diode is also provided.There is no danger from surge voltages generated from load
inductance or parasitic inductance.
Due to the presence of high voltages I would like to use further protection
for the MOSFET.
Should you help me please?

Best regards

Theodore