That makes perfect sense. I thought you were doing it to benefit the tree. But, definitely do what makes you safe!!!
But if you had some pears this year then obviously pollination is happening. Last year may have been a year the bees didn't come around. We had that problem this year. We...
Hmmm...one more thought. I would compost your duck poo with some straw or grass and then put it under the tree. I don't scoop up my chicken poo and put it there, but because they live there they leave little pods of fertilizer from time to time.
You are not going to lose this tree. I wouldn't change anything with a retaining wall. That tree has been there a long time with no RW. I do think the duck poo will do the same thing as the stakes. The most effective thing you can do for the tree is to prune it. I agree with the 1/3 rule...