g'day mc,

you could go along the 'good neighbour' line, over a cup of tea or
such point out the minor discrepancy, and maybe offer to buy another
palm of similar ilk for them to plant in their garden.

can't see anything wrong with being neighbourly, and if it is a common
fence line then the neighbour has right to pay 1/2 the cost of a fence
of the acceptable standard of the nighbourhood.

let us know the outcome hey? hoping it will be win/win all round?

snipped
With peace and brightest of blessings,

len

--
"Be Content With What You Have And
May You Find Serenity and Tranquillity In
A World That You May Not Understand."

http://www.gardenlen.com