Bg 2.67

indriyanam hi caratam
yan mano ’nuvidhiyate
tad asya harati prajnam
vayur navam ivambhasi

Word for word: 
indriyanam — of the senses; hi — certainly; caratam — while roaming; yat — with which; manah — the mind; anuvidhiyate — becomes constantly engaged; tat — that; asya — his; harati — takes away; prajnam — intelligence; vayuh — wind; navam — a boat; iva — like; ambhasi — on the water.

Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
As a strong wind sweeps away a boat on the water, even one of the roaming senses on which the mind focuses can carry away a man’s intelligence.

Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Unless all of the senses are engaged in the service of the Lord, even one of them engaged in sense gratification can deviate the devotee from the path of transcendental advancement. As mentioned in the life of Maharaja Ambarisa, all of the senses must be engaged in Krishna consciousness, for that is the correct technique for controlling the mind.