At what size is my horsfield tortoise safe to be outside in an uncovered pen?

[Coffeg]

Hi I have a 2 year old 8 cm horsfield tortoise which we bought last year. For his grist year with us we kept him in a large guinea pig run with hearing lighting etc and put him outside in a small covered pen on the very warmest days. However I don't like seeing tortoises caged and I'm keen to get him outside all summer. His new enclosure is large, surrounded by log roll and has suitable housing etc. my only concern is his size and whether he is still vunerable to attack. I would imagine he is way to big for a bird to carry off but not sure about a nothing else. The garden is secure but I guess a cat etc could get in. As it will be his first summer outside I'd be grateful for any advice. Thanks