Roulette is a viable option. The is a good "guaranteed strategy" but does require quite a big bank balance. Can be slow to start and risky.
Some sites allow you to spin without betting. so you can force sequences of say 5+ reds in a row.
For example, hitting the same color for
n times in a row on a single-zero roulette has the probability
For
n = 3, this is 11.51%,
For
n = 5 is 2.72%,
For n = 10 it goes down to 0.07%.
So if you Start with a Bet of £1 on a 5 Sequence. If it Wins = £1 Profit. If it loses you double your bet to £2, again if it loses double again to £4 and so on. Once you hit a win your profit will be equal to your starting bet.
I done this on small scale and made £60 in a few days, then got greedy had a few unlucky spells of 10+ coloured runs followed by a "Zero" Green. So set yourself a limit of say doubling you bet 5 times. If no win start again.
But remember some tables have bet limits so do it wisely and it can take a lot time to get sequences to bet on.
a £1 starting bet can easily become very large if you hit a run of 10+ sequence
1-2-4-8-16-32-64-128-256-512