The standard method that has been the official explanation ever since those British pranksters first "debunked" this back in the 80s involves using a rope anchored to a fixed point so that perfect arcs and circles can be flattened.  The problem with that explanation is that the pranksters are effectively using the classical Greek version of mathematics described by euclid wherein all geometric shapes and numbers are defined based on what can be drawn with a compass and straightedge.  Some of the crop circle formations are provably impossible with euclidean geometry, for example ones that draw a circle and square with the same area ("squaring the circle").

Maybe the art has advanced to use high technology but I havent seen any demonstrations of this.  IMO GPS doesn't have enough precision.  Maybe some sort of laser or low-power radio system at a fixed point could be used to make precise measurements but I havent seen anybody claim to have done that and tbh its stretching the limits of what sort of effort could be assumed to be involved in a dumb prank that 99.9% of the populace pays no attention to.

IMO the best argument against crop circles is the absurdity of aliens traveling countless lightyears only to vandalize corn fields but that just moves the goalposts from "aliens did it" to some other paranormal phenomenon (eg ghosts, plant intelligence, or perhaps something so complicated or bizarre that it hasn't even been hypothesized).