It depends on the way your pond is situated but I think I would simply divide into one -restricted, fenced, locked gate adult- side with the pond and the other -safe, babyproofed- side with the play area.
This way, you can also thoroughly examine all the plants, structures, etc. in the play area side for anything toxic or hazardous and eliminate them before your baby becomes mobile. Of course you would still supervise and stay with your baby (and friends) while she/they are outside, and I urge you to start teaching them how to recognize toxic or dangerous plants as soon as they can learn.
When my DDs were little one fun game we used to play is to send them off to gather leaves or berries from the garden and compare shapes, textures, colors, fragrances. One variation was specific -- gather leaves that has more than just a "green" smell. Or gather flowers that smell nice. Of course by the time we were playing this game, my DDs knew how to recognize poison ivy and other rash-causing plants, thorny plants that shouldn't be grabbed, berries that shouldn't be touched, can be touched but not put in mouth, etc. And absolutely the first thing on going inside was to troop to the bathroom and thoroughly wash hands before eating anything.
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