Hi, I use a longline (literally a lead with clip to go on collar) when I take Odie to the park. His recall is fine when we are out on walks where we meet no dogs but his selective hearing comes into play when he spots a dog! I am able to grab him a bit easier when a long lead is training behind him

I think they are available in PAH in 2 sizes or maybe Ebay have them? You could walk him on your usual lead until you want to practice recall then slip the longline on. Oh, I also use a whistle for recall too.
The extendable leads are sometimes lethal, my poor daughter got slashed across the back of the knee in the summer when Odie abruptly done a u-turn and tangled her up

She still has a small scar

You also can't let an extendable lead trail as it would be dangerous. Lesley