Letting my cat out

So my kitten is 6 months old, he’s been exploring the garden for around 2 months, he’s been neutered, fleed, wormed and microchip and is upto date with vaccines. He’s recently started climbing the fences of the garden n looks ready to go off exploring! I’m just so scared he won’t come back, is there any tips people can give to stop my anxieties and to ensure he returns