Green’s Dictionary of Slang

klip v.

[Afk. klip, a small rock]

(S.Afr.) to place a stone under a vehicle’s wheel to stop it running away downhill.

H.A. Roche On Trek in Transvaal 91: Crawling into the asagin, the wheels of which were ‘klipped’ to keep us from running down the hill.
[SA]C. Pettman Africanderisms.