articulated feet work really well, have never needed spikes on soft ground, I just embed the ladder feet in to the grass or earth.
Ladder slippage always a risk, the more safeguards you put in the more you reduce the risk, but then you have to balance that with the time it takes you to do your job.
The average window, once you are in place, will take you about 90 seconds to clean. Some of the things you can get to stabilise ladders are really first rate, great if you are a painter and decorator spending 25 minutes painting a window
Not quite so functional when you are hoping to only take 20 minutes to clean all of the windows on the house
I rarely use the 1 for 4 rule, guess that after 20 years as a window cleaner and prior to that, 12 years on ladders as a decorator, you instinctively know what is safe and what isn't.
There are occasions when you need the ladder so steep that you need pitons to climb it
If the ladder slipped then it was not set steep enough for the conditions.
But the addition of articulated feet to your ladders will make an enourmous difference, and is possibly the simplest thing you can do other than have someone footing the ladder for you
Personally I always like someone footing the ladder for me...................meant that if I did fall off there was going to be someone there to break my fall
and at 15 stone that takes some breaking!! :-/
Now I use WFP, so that isn't going to be a problem for me anymore
Ian