Question
My Mayer Lemon tree has provided lots of very large lemons.  It is looking a little puny lately, the leaves are yellowing.  Sometimes the lemons are deformed.  Also, something is eating the lemons. I see a pealed lemon on the ground. I suspect rats, but don't know.  Is there anything that I can do to discourage the rats or whatever?

And, what is the best thing to feed the tree?

Answer
An acid fertilizer with a higher nitrogen content, lower phosphorus,and a medium potassium would be a good fertilizer. An azalia fertilizer which would be something like a 30-10-10 would also be ok. A fertilizer with a ratio of 5-1-3 would be perfect but will be hard to find. Citrus are really not all that fussy and most acid type fertilizers will work. Be sure to purchase a fertilizer that also contains all the common trace minerals.
For the rats I would suggest putting out a trap and see what you catch and then you can detremine what is eating the fruit and control the pests.