With hydrochloric acid, nitroglycerin, Sarin, CS gas like Janet Reno used on David Koresh - what? I'm open to any of those, unless you have a better idea.
Water is great for drowning Rats.
A large Lake Trump fed by the Rio Grande, would make a nice reservoir! Also, a Lake Pence would work for me.
Parks with gun ranges, for long range, scoped, rifles.