Ahhh Your dog has turned into a teenager ;) It's not your fault it happens to most of them ;)
Mine did the same at 7 months, only it happened while we were at an unfenced field (the usual round here) she spied a man in the distance and shot off, I called - nothing, I called and ran - nothing :( I was terrified I'd never see her again or she's be hit by a car :( eventually she got fed up as the man didn't want anything to do with her and just shoo'd her away, but by then she was a 1/4 mile away in a street

Luckily she ran back on the field and wanted to find me (I almost fainted with relief when she eventually came back) Once she was on lead I made a BIG FUSS (even tho at that point I wanted to do anything but) and then 10 mins later I tied her to a lamppost and went and hid from her about 10 yards away - no-one else around at this point. After a few mins she was frantic ;) so I went back and got her. I wanted her to know that she
really wanted to be with me ;)
Like you tho I've kept her on lead for the last few weeks as I was terrified she'd go again. Yesterday I let her off with my others and she was fine but no-one about ;)
We'll be back to training in tandem and running her between me and son for the next few months (one holding her and the other calling ;) ) until she's had a season and is over the KEVIN stage ;)
In your position I'd have him on a long line and take him out hungry ;) that way he'll be more interested in the chicken/cheese/ sausage you have for him ;)