In the case of using " assist " hook at the eyelet of the lure , I use rubber band secured to the head of the lure to prevent the flailing cord with hook to foul the leader , not sure if this matters but certainly give me a peace of mind .
On leader for tuna and in my case YFT in Indian Ocean , when the schools contain 100 lbs. tuna I use minimum 100 lbs. mono leader but there are occasions the tuna bit this thin leader so if they are not shy and will take bigger lures , will include a short 200 lbs. fluorocarbon bite leader some 8" long to prevent a bite thru . Not sure about BFT but YFTs have small teeths that can cut thru small leader in no time .
The length of the mono leader I use is the same as when fishing for GT , approx. twice the distance from the reel to the rod tip . This helps the " wireman " to take the leader upon landing the fish and in many cases during tuna fishing , due to the way tuna fights the leader may be wrapped around the tail and braid may be frayed by the tail if the leader isn't long enough .
Jon .