A modular flexible fencing system, configured for installation by a novice without special tools, equipped with a novel flexible fencing material retention system which employs caged receivers that interface with spring-equipped auto-tensioning inserts disposed on the termini of each instance of flexible fencing material. The auto-tensioning inserts ensure that adequate tension is applied to the flexible fencing material with minimal adjustment. U-shaped posts are equipped with a slot that ensures the caged receivers are secured within the posts at the desired positions. Screws further ensure that the caged receivers are mounted in place securely.