Despite making seven signings already this summer, Southampton are far from done in the transfer market. So far, Russell Martin‘s focus has been very much on defensive reinforcements, with five of the seven incomings playing in the backline and another Flynn Downes’ £18 million arrival who tends to operate just in front of the defence. The other is Adam Lallana, the 36-year-old who has returned to his first club a decade after leaving for Liverpool. Despite the fact Southampton have already welcomed three centre-backs this summer – and a left-back who can also play centre-back in Charlie Taylo…