I read that it is common/possible for investors to ask for anti-dilution clauses.
Is there a way a co-founder can protect himself against dilution? Of course, dilution will eventually happen during later rounds of financing, but it is possible/common for example to require that all co-founders are equally diluted in later round of financing?
Update The specific case could be that some shares are issued and they're distributed to investors and some, not all, cofounders (f.i. as a bonus). In this case the other cofounders (the ones that didn't received shares) are more diluted than the others.
Is that possible? In the case, how can someone prevent that?
What you're suggesting is mathematically impossible.
First, let's start by looking at how an anti-dilution clause works by using a super simple example.
Now, if you're asking "how can you make sure all the co-founders are equally diluted," well, that's essentially automatic. Everyone without an anti-dilution right will naturally end up owning a smaller percentage of the company, equally, when new shares are issued.
This is just the nature of how percentages work; it has nothing to do with startup finance :)