Two opinions, depending on your "control" of the bar. (If it is a catered meal and you are choosing to have a bar available, you are "in control" of the bar; if it is a restaurant setting, where the bar is available regardless, you are not "in control" of the bar.)
If this is a catered meal - as in, an event where you have selected the menu that will be served similar to a wedding reception - then don't offer alcohol at all, or go the wedding route with "wine and beer only." Then set a cap such as two glasses per guests or whatever, arranged ahead of time with your bartending/serving staff. They will know how to gracefully decline a guest who tries to get a glass beyond your cap. This also solves the issue of a family member who gets obnoxious when they have overindulged. No one gets targeted or singled out because everyone has the same cap, and no one has the option to buy more past the cap and still end up making a fool of themselves. (I don't believe it is appropriate to offer a cash bar. Cash bars are very regional, but if you are "in control" of the bar, then I don't think it's appropriate to make guests pay for drinks.) Also, if you choose to forego booze altogether, don't be bullied into making it a daytime meal because "people expect alcohol at night" - they can go hit the bars afterward if they "expect" alcohol. Their alcohol dependency is not your responsibility.
If this is a dinner as in you are simply all going to a restaurant together, where guests will select their own meals from the standard menu provided by the venue and you are picking up the tab, then absolutely do not hesitate to specify that you are not funding anyone's booze. I am appalled that people think this is an obligation. That is hideously rude, in my opinion. When I am invited to dinners in this manner where a host has graciously offered to pay for my meal where I would otherwise be paying for it myself, I ALWAYS offer to pay for my own drinks, and would never assume that the host was paying for my libations.