Turtles are known as one of the slowest creatures in the world so does Spineback Turtle. I play splinterlands almost 2 years and i don't remember when i used this card last time so i wanted to give this card a try to see how it does perform in battles. So best rulesets to use this card in my opinion are reversed speed 
and Little League
. Because this monster is so slow in "Reversed Speed" ruleset this card gets faster and in "Little Lague" ruleset Spineback Turtle is the best tank to use in water team in my opinion.
ABOUT LINEUP
As a summoner i used level 2 Vera Slacia.
It's a great summoner to defeat enemy who use lots of monsters withflying ability.
As a tank i used level 3 Spineback Turtle. At level 3 this card has 7 health and 3 shield which is a good stat for 4 mana card.
In order to make my defense even stronger i used level 3 Flying Squid at second position. This card can attack from second postion,does 3 damage to enemy has good health to replace tank if the tank gets killed.
There's a saying that attack is the best form of defence so to make my attack stronger and to ptotect my monsters from enemy monsters which has opportunity ability i used Deeplurker. At level 3 this monster does 3 damage which is enough to take down enemy's low health monsters with just one attack unless they have shield.
In order to elliminate enemy's monsters at back positions i used level 3 Sabre Shark. At level 3 this monster does 2 damage and has good enough speed to not miss attacks.
At last position i used level 1 Albatros to protect other monsters from sneak attacks.
BATTLE SUMMARY
Using a summoner with snare ability worked well for me because enemy team used lots of summoners with flying ability. At first round 2 of the enemy's monsters got killed with just a single attack.
At second round i lost the main tank Spineback Turtle but managed to kill Tower Griffin. At round 2 monsters left face to face to fight each other but both of my and enemy's monsters stayed alive. At final round after taking down LIving Lava i won the match easily!
Her's the battle link if you are interested to watch the battle and thanks for reading!
https://splinterlands.com/?p=battle&id=sl_11ee0c2ae1ea4453abb23d52c16f6293
All the pictures used in this post are taken from Splinterlands website.