However, in a margin account, you can write uncovered calls on a margin loan. (thecollegeinvestor.com)
Because there's no limit to how high a stock price can rise, there's no limit to the amount of money you could lose writing uncovered calls. (investor.vanguard.com)
Some lesser known alternatives include currencies (excluding digital currencies like Bitcoin); mortgages (which can include your own mortgage); precious metals (like gold and silver bullion); private market investments (including specified small business corporation shares and exempt market securities); options (although CRA warns about writing uncovered call options or put options); and annuities (which are finally becoming more attractive as interest rates rise). (moneysense.ca)