Throw a sheet over it, demand it be taken down and start a "Museum of Shame", or something to that effect.
Now that history will be a little more forgotten - or never known to some.
I agree that such statues should be removed by lawful means and that is the way in which I personally would go about doing so.
I'm not in agreement with the notion that statues are a valid means of teaching history though. Rather, they tend to glorify whatever the subject did. To erect a statue to somebody is a form of public recognition. Of tacit approval.
The Empire is widely taught in British schools as a history subject and it's pretty well known what our record was where slavery is concerned. The best known of all the figures involved in slavery is William Wilberforce..... who was an anti-slavery campaigner...!!
I don't think anybody is going to tear down any of the monuments or statues erected to his memory.
Also..... it can be argued that the removal of Colston's statue by forcible means has already provoked a response.
A statue of Robert Milligan, another historic slave trader, has been removed from outside the London Docklands Museum. This removal was legal and ordered by the Mayor of London, Sadiq Khan.
Statue of Robert Milligan Removed
No controversy there, then. It's disappointing that it takes an act of vandalism by demonstrators to set in motion other removals by legitimate means. I would rather these monuments to the likes of Cecil Rhodes Robert Clive among other imperialists had been done long ago.
Hopefully, we are now seeing a sea-change in attitude towards the Empire.