If you don't forget, you don't get fined - simple. I'm not convinced that checking your account is any more difficult than checking you've got a couple of quid handy before you set off.
I do agree that there should be an option for getting a reminder / being able to top up once your account...
You can set your account to manual top-up and only pay in your £10 when you need to (i.e. when you've got less than £1.67 in your account). That's what I've done - also prevents them being able to mis-charge you any more than £10.