I have a weedy garlic too (not A. triquetium, the one with thinner grassy leaves). Unfortunately I haven't got an easy solution. I dig out what I can and repeatedly pull/cut the foliage off what I can't, the theory being that it will eventually weaken them, same as the pesky spanish bluebells.
Similarly to Jenny, my invasive allium isn't allium triquetium but the thin-leaved one. I dig out and dispose of as much as possible in areas I'm replanting and try not to transfer it around the garden. I've been here 14 years now, and haven't eradicated it but honestly I don't try that hard. I have enough to do with the ground elder, bindweed and horsetail elsewhere. My mum has been managing invasive muscari for years and used to attempt zero tolerance but the tiny bulbs always win.
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Similarly to Jenny, my invasive allium isn't allium triquetium but the thin-leaved one. I dig out and dispose of as much as possible in areas I'm replanting and try not to transfer it around the garden. I've been here 14 years now, and haven't eradicated it but honestly I don't try that hard. I have enough to do with the ground elder, bindweed and horsetail elsewhere. My mum has been managing invasive muscari for years and used to attempt zero tolerance but the tiny bulbs always win.