Best way to use my £50GBP Loss Only Bet offer from Betfair tonight?? Any ideas?

I have received a £50GBP Loss Only bet offer from Betfair* that needs to by used by midnight and wondered if anyone had any suggestions as to the best way to employ it?

I would quite like to make some guaranteed profit if possible!!!! I can use (and lose) up to £50 in backer's stakes if I lay, so any ideas on the best market to maybe bet and lay on tonight to get a good return?

Blurb says "If you place a bet or multiple bets on any markets you will receive your stake and your profit from these bets as normal. Any losing bets you place during the promotional period will be refunded into your account".

Any assistance would be greatly appreciated!!!