It is true that, when the marches are sent,  if both towns are shielded ,there is no battle,   

Only the one who isn't shielded knows otherwise, unless the opponent is luckly enough to see  shielding occur.

In any  case, no battle, doesn't mean no conflict.

Players will object to others who are, in their opinon, claim jumping. 

It's a war game, and some take it more to heart, especially if they had a bad day at the office.

Though what you suggest  could be a solution, it doesn't help if it shows no one going to a tile and you think you are home free, if after you send, someone moving faster or is closer gets there before you do. Any notification of 'tile under attack' could be ignored.

If you are on global view you do see if others are heading to the same place, but who's track appeared first, and who will get there first?

Gold is more plentiful than it was , but it can still take a time to build up a stock, such that  it is affordable to keep the town shielded.