Backing with the intention to Lay- any rules?

Think about what you're doing and do it.

If you're backing a 20/1 shot because you want to lay off at 6/1, then unless something massive has changed when it hits 6/1 (presumably it hits 6/1 too early because that's why you've backed it to lay in the first place), then lay it. If you're not laying at this point most of the time, you're overstaking, as you've likely bet bigger because you're laying off later.

For the sake of argument let's say a 20/1 shot goes to 6/1 about once in three. You can bet a lot bigger on a 2/1 shot than a 20/1 shot, so if you don't do what you said, you'll go bust in the long run.

Also define your downside. Are you letting the whole bet run to 6/1, or are you bailing out if something goes wrong and it hits 50/1. If you've made this decision in advance, then you won't have that "Blah, it's only a few quid, I'll let it right" moment and waste money when it gets there.

I guess you can already see by a couple of posts why i chose this name back in my poker days ;).

Thanks for your feedback Lori. What happened was it actually went down to 2.6ish on betfair and i thought it had a good chance of winning so got a little greedy and thought i would let it get closer to 2 before I would lay (if at all), howver the day before the event was closing the price started going out again hence why i had to lay at 6/1 to ensure if it didn't come in I would lose 0. However this ate into any potential profit by approx 27%.

That's key imo with those bets.

You make the plan when you're thinking clearly about the bet, so it's likely pretty good.