Like a tortoise withdrawing its limbs, the yogi must withdraw the senses from sense objects, as taught in the Bhagavad-gita (2.58-61). The Bhagavad-gita (6.24-26) teaches that this doesn't mean suppression but proper engagement in spiritual activities. When senses are engaged in devotional service, they naturally become controlled. The positive method is devotional engagement rather than mere sense suppression.