As a vector for the introduction of nonnative species, why is hull fouling particularly difficult to combat?

It is difficult to combat because hull fouling is unintentional

Explanation:

Since hull fouling is unintentional deposits on non-native species into an environment, meaning it is accidental and one may not necessarily know they are introducing a non-native species.  The term comes from when originally non-native species were introduced unintentional, unknowingly and accidentally by attaching themselves to the hulls of ships in one ecosystem where they are native, then traveling and being deposited/inroduced, unintentionally and unknowingly, into the new ecosystem where the species is not native.  Since the non-native species is introduced unintentionally, accidentally and often unknowingly, makes it difficult to detect and control the non-native species, making it particularly difficult and hard to combat and or prevent.

the abdomen (less formally called the belly, stomach, tummy or midriff) constitutes the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. the region occupied by the abdomen is termed the abdominal cavity. the stomach secretes acid and enzymes that digest food. ridges of muscle tissue called rugae line the stomach. the stomach muscles contract periodically, churning food to enhance digestion. the pyloric sphincter is a muscular valve that opens to allow food to pass from the stomach to the small intestine.