If there is the slightest possibility that a cutter, ON ANY MACHINE is likely to climb mill then it is essential that the workpiece is secured so that it can't move away from the cutter or be pulled along as though it was a gear rack by the rotating cutting edge.
Even on heavy duty Machine shop equipment it is very few machines that have the machining table and driving leadscrews set up or configured to allow safe climb milling with a horizontal cutter and why stuff is always clamped securely to a table with good side jib settings when using an endmill (router cutter equivalent).
Think about what would happen if you tried to cut a piece of wood on your table saw from the rear rather than the front.
When you are trenching with a router, the cutter will always be trying to climb in the opposite direction to its rotation and the router and workpiece regardless of whether hand held or table mounted must be constrained in such a way to prevent the two moving sideways and allowing the cutter to dictate the results.
You may get away with not bothering to consider this for some considerable time dependant upon the wood type and grain direction of pieces being routed but the day you wreck the only piece you had to finish a job or remove a few finger tips because the cutter took charge is the day you will remember these comments.
