14 month old will not sit in the bath!

From the moment he learned to stand--literally 5+ months ago--my little guy has refused to sit down in the bath. This has resulted in me needing to get in the bath with him. We have a non-slip mat, but even that doesn't cover every inch of exposed tub. He has slipped before and remains undaunted at standing and walking in the tub. He loves the bath in general, but just won't sit down! Any advice anyone can offer?