A very good question - and one that occupies my mind many times. Firstly, as far as I know, I don't have any poisonous plants - but if anyone on the forum spots any, please let me know. I have some stray blackberry threads that come from neighbours but mu buns never seem to bother with those. There's some ivy - again from neighbours, and some hawthorn (neighbours again). The garden has the odd bluebell which as far as I know, being a bulb, can be harmful but they've never been eaten by my buns. There's roses and I've got some blackcurrent and raspberry bushes which never get touched by the buns. There's a pear tree but they don't bother with that either. There's some triffids which I have no idea what, and a few flowers but the bunnies seem to know what to munch on and what not to.
Predators? Now, there's a interesting one. About 18 months ago, some local bird keeper about 30 miles away, lost his 'pet' falcon that never came back. That sort of bothered me and worried me about other rabbit keepers because it was not an indigenous species round here and I felt it was very reckless of the bird keeper to endanger other pets that would otherwise not get threatened. Foxes? We've heard of foxes in a village not far away - about 4-5 miles. They're urban and apparently they can climb or jump high fences. Our fences are 6 foot one side, and the other side with bushes and hawthorn, pretty impregnable. Cats have been an issue and I've been seen on a few occasions running up the garden waving my arms like a maniac as the odd one strayed into our garden and on one occasion was stalking my bridge buns Ben & Georgina (Ben was considerably larger than the cat but that wasn't stopping the cat). Thankfully and for reasons I don't know, the cats have ceased coming in the garden but there is at least one in the area.
I keep an eye on the garden and rabbits as much as I can and when it gets to 5-6pm, it's coming in time for the rabbits. Twighlight is the favorite time but also when they are at their most vulnerable so my duty is to protect them as much as I am capable of.