Briefly describe this fundraising event:
Critter plop on a square of an athletic field makes one ticket holder a lucky winner of cash and/or prizes. Cash is more easily divided if necessary.

This is a little tough to implement in the heart of the city, and impossible to fully describe, but ya'll will "get the drift" and maybe other sources (internet search?) can "clear the air" about some details. There are, of course, regulations in regards to care of the animal involved, and likely state auditing of the books. It is in essence a lottery, so it's definitely subject to regulation.

Organizing the event:
Find out about those legal issues first. Choose a large field, hopefully with stands for the peaceful party animals (humans) to wait for the miracle moment.
Grids are chalked onto the field and numbered. Tickets have to be sold corresponding to those grid numbers, and the length of time that takes varies according to community size, publicity, volunteer enthusiasm, etc. Days to weeks?

A docile critter is selected, groomed resplendently, and on the appointed day and time, is fed and watered and let to the field to determine the winner. No one is allowed to influence this random event in any way. This can take either a short time, or a good long while, and some groups find it a good time to sell concessions like hot chocolate, popcorn, and hot dogs. There may be other entertainment on hand as well.

The size of the squares on the grid matters, and because it is still possible that more than one square will be ... chosen, it is really crucial that the rules be clear and the judgement impartial.

Capital possibilities:
Tee-Hee! I suppose they are almost endless...

This fund-raising method is not everyone's cup o' tea, but it sure gets attention from media. I have read about it being done twice as a band booster event.

Degree of difficulty:
Probably no more strenuous than the average big event. Involves many volunteers, though.
It might be wise to have more than one target date, due to weather being not wholly predictable.

Other suggestions or comments:
I think I've about "covered" it.