We used to let out about 6 acres for horse grazing on an 11 month basis for 500quid. The agreement was that they would top the weeds, keep the fencing in good order and rotate the grazing so that it didn't get destroyed. They didn't top it, didn't look after the fencing and didn't strip graze so the land became a weedy mess after 2 years. To cap it all I found out they were about to sub let it. We're now in the process of getting it back into good order still finding bits of horse rug and other crap. And there'es now ragwort here and there which there never was before. Result, goodbye horses.