True, but it's rare to get a margin call on a house.
you get a sort of margin call when you don't pay the mortgage.
These days is quite safe to play on gold futures and you would need 1000$ on your account to trade 100,000$, so, if it gets to 101k$ you double and if you get to 99k you lose the lot.
another good thing would be that if you have 100k you can put 99k in a saving account and you get 4-5% interest and you top up the money in case you risk the margin call on gold. It is probably a good way to make money from holding gold. the risk is that if the world gets in real trouble that gold could disappear once the exchange backing it is insolvent. But I believe you have that sort of risk also on etf and even holding a home