I just remembered Aesop's fable of the crow and the pitcher. Fill the drain with concrete; the concrete will displace the water to the top thus rising the tennis ball; just pluck the tennis ball out and then consider how to get rid of the concrete in the drain.
saga over - just gone down there - folded a rubbery mat in 4 - knelt down and got it out and was able to get up no problem. Whee - thanks folks for your kind ideas.
When I couldn't get up that last time it was only 2 months after my accident but as long as knees were on something comfortable ie the mat - I got up quite well.
mamy - there is a drain over it altho it's not secure but I am going to go over the yard and remove all balls. bye for now - away down for a wee cuppa.
I have only just seen and read this from start to finish. What a saga. But I want to thank you all for giving me a laugh to start my day.
So glad everything got sorted with no harm to anyone's knees ( I know the feeling) or other bits.
Thanks all you made my day.