What are things i can legally do in a custody issue to prevent father from gettin any type of custody?

he was in prison for 5 years over drugs and they still saying he has a strong chance i dont feel comfertable considering he only been round the past 7-8 months. my son is 8 yrs old. and even 4 months ago he didnt know his b-day yr born or even hid fav. color.