Sidebar 1: The Inca empire of South America did not have money or currency. Taxes were paid as labor or as merchandise such as agricultural produce. One tribe was so poor that that the Incas levied a tax where they were required to pay a certain number of dead fleas every year.
Sidebar 2: According to R.A. Oliver in his book The African Middle Ages, 1400-1800 the expansion of the Asante Empire was primarily fueled non-native inputs like horses and firearms which were paid for by captives (sold for slaves), gold and diamonds.
Neither horses or firearms were "durable" in the climate of Benin, Togo, Ghana and Nigeria. That region had no indigenous, large, traction animals due to endemic diseases. Horses did not last long. Firearms firing corrosive black-powder soon had their touch-holes rusted shut in the oppressive heat and humidity.
A secondary factor that fueled the expansion of the Asante Empire was the primary agricultural model shifted from slash-and-burn (academics prefer the term 'midden') agriculture with cassava, yams and plantain as the primary crops to heavy-hoe/grain (primarily sorghum) as a crop.
Oliver observes that it is difficult to overestimate the impact grain has on warfare as no other food is as compact, as transportable and as non-perishable as grain. Can you imagine trying to wage war if your only source of food was turnips or sweet potatoes (especially if you had no draft animals)?
History can teach us much if we pay attention.
One of the advantages that potatoes had for the poor Irish was that, unlike a field of barley, potatoes were not damaged by a party of fox hunters or soldiers riding horses over the field.
Raiders and looters are looking for grab-and-go food. Foods that need to be dug are at the bottom of their list. Foods that are 80%-to-90% water are at the bottom of their list.
Corn and wheat fields are instantly recognizable. Potatoes, turnips, carrots and the like are much less recognizable (especially if there are a few weeds in the field) and require that the raiders be much closer before recognizing what they are.
Theft as a tax
If you think about theft as a tax, then it changes your mindset to determining ways to minimize the tax.
Is a small amount of petty larceny, like neighbor kids lifting a few watermelons every summer, the lowest tax?
Is paying "protection money" to local strongmen the lowest tax? It might be if they enforce their monopoly and suppress vandals, raiders and outsiders.
Is dedicating 30% of your workforce to guarding the fields the lowest tax? It might be if you have a bunch of old men who are otherwise unsuited to field work.
Offer value-added alternatives
This is a little bit out-of-the-box and may sound naive, but what if you offered to cook and serve the hungry boys (the raiders) a mess of cheese omelets and hash-browns in exchange for leaving your chickens and milch animals alone? It could even be a standing offer: Any time the raiders swing by they get a discount on breakfast, much like cops get free donuts.
"But they will eat everything I have!" you protest.
I suspect that if you tell the "boys" that you are running short of firewood, they will gladly "find" some while you are mixing up and cooking their omelets or flap-jacks. In a similar way, if you start running low on food, if you whisper into the ear of the leader, they will bring food to supplement what you are cooking for them.
That might be at odds with their standing orders but HQ does not need to know about everything that goes out in the field.
There are other value-added propositions. Can you brew anything resembling beer out of native materials? As long as you accept that (heavy) taxes are inevitable, then your farm/craft center will become a destination for grain and food resources instead of a net exporter of them.
Atrocities will undoubtedly happen, but not as ubiquitously as the entertainment industry would have you think. Mass slaughter makes for good entertainment but very bad economics.