Habitat Upgrade

About 4 years ago I found a little half dollar-sized red eared slider flipped over on his back in a parking lot being circled by birds. He was still alive but covered in ants. I brought him home and he’s been living a pretty good life in a 55 gallon tank ever since, I just worry about enrichment for his little turtle brain sometimes.

Well fast-forward, he is getting bigger now and it’s looking like time for an upgrade on his habitat. Here are my 2 options, let me know what you think would be best:

Upgrade to 100 gal tank \- simple enough \-takes up a lot of space in the house (we already have a 100gal saltwater tank as well, so this would be huge tank #2)

Outdoor custom built turtle pond \- might give him more enrichment and a happier life, though we would have to make sure to spend time with him out there because he does enjoy seeing the fam \-more exposure to dangerous elements. I am not sure how best to protect the pond, I’m thinking like chicken wire and a shade spot \-I live in a tropical area where we only get maybe 4 nights below freezing a year, so we should be fine with a simple outdoor water heater in winter right?

TLDR; which setup would be the best and/or least stressful change for my red eared slider? Upgrading the tank or building him a pond?