rubber heel1
/rʌbə ˈhiːl/noun
1A shoe heel made of rubber.
2 Slang. A person who investigates the conduct of members of his or her own organization; specifically an internal police investigator.
Origin
Mid 19th century. From rubber + heel.
rubber-heel2
/ˈrʌbəhiːl/verb
[no object] To wear shoes with rubber heels; (hence) to keep a person under surveillance, to spy on. Also with object: to investigate (a colleague), to keep (an associate) under surveillance.
Origin
Early 20th century. From rubber heel.