Chock the wheels before unhitching.
READING GUIDECAMPSITE STABILITY
Wheel Chocks vs X-Chocks
What conventional wheel chocks and between-tire stabilizers actually do, and why they are not interchangeable.
Conventional wheel chocks are the primary tool for preventing a parked trailer from rolling. Between-tire products such as X-style stabilizers can reduce movement on tandem-axle trailers, but they should not replace proper wheel chocking.
What matters in practice
Between-tire stabilizers only apply to compatible tandem-axle spacing.
Do not treat a stabilizer as a substitute for a wheel-securing device.