leesh and fin advise

my surfing has been progressing quite nicely but ive been finding it hard to keep control of the board when i get on the nose i ride a 9'2 NSP longboard you could say thats the problem being a cheap pop out but its acctully a pretty good board, i have a 8" (i think) fin with it as far back in the box as it will go but when i get on the nose the board i find it really unstable and tends to slide out alot, would geting a large fat 10" single fin help me hold it on the nose easyer?
plus i broke my leash today was considering a knee leash do any of you use them or would it be best to stick to the tradional leashes
plus i broke my leash today was considering a knee leash do any of you use them or would it be best to stick to the tradional leashes