If there is marker (ink) on the fence you will need to remove it or cover it with something before you paint over it. If you don't the ink will bleed through the paint.
Unfortunately this will probably mean using a solvent of some description which will in turn remove the paint on the fence, but you have to re paint anyway so no biggy.
The spray paint should be ok to paint straight over unless it is oil based (enamel like Kill rust etc) in which case do the same as above.
HTH
Cheers
Mick
1999 Land Rover 110 Defender TD5 Cab Chassis
1985 Land Rover 110 County 4.6 EFI V8
1993 Track Trailer camper
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