If a narrow strip around the perimeter of your protected area can be de-vegetated, you may be able to use an electric fence. The lowest wire would need to be 1 1/2 inches from the ground. That, plus two more wires 2 1/2 inches apart may be all that is needed.
A 6 foot tall smooth continuous wooden-board (smooth-surfaced on one side, or of plywood) fence would work too. But in Panama it might decay too soon.
Can you find a cheaper form of repellent that isn't advertised for such a specific purpose? I think there is Bitter Apple out there for repelling puppies from chewing on furniture. Maybe you could get the active ingredient in bulk and spray it on with a garden sprayer.
Maybe there is cow repellant available somewhere.