In my garden Bathtub i have goldfish and early summer they like to splash and spawn in the shallow near the edge. I had a few jump out in the past. SInce than i always cover that side with a mesh about 20x20mm grit.. This Year i found a young frog, dead and dried out in a simmular way. Got stuck in the mesh.. I made pictures from it alive and well a few days before.. Next year i need to make it from acrylic panel.
Careful with acrylic it can raise the temperature of the water. I did a similar thing last year on my outdoor ceramic pond. I drilled loads of holes in it to allow evaporation and avoid heat accumulation but it didn’t stop the water from warming up quite a bit. I lost a lot of guppies and the goldfish were not so happy but recovered. Never used that acrilic panel again. Now me thinks if the fish just wants to jump then be it.
You could look at floating anti-heron grids Marcel - they are a quite big spaced grid that float on top should keep fish underneath but let a frog etc. through.